Bsi bs en 00625 1996 (1999)

BRITISH STANDARD

Gas-fired central
heating boilers —
Specific requirements
for the domestic hot
water operation of
combination boilers of
nominal heat input not
exceeding 70 kw

The European Standard EN 625:1995 has the status of a
British Standard

BS EN
625:1996


BS EN 625:1996

Committees responsible for this
British Standard
The preparation of this British Standard was entrusted to Technical
Committee GSE/29, Domestic gas-fired central heating boilers, upon which the
following bodies were represented:
Association of Manufacturers of Domestic Unvented Supply Systems
Equipment (MODUSSE)
Boilers and Radiator Manufacturers’ Association Limited
British Gas plc
Department of the Environment (Building Research Establishment)
Department of the Environment (Property and Buildings Directorate)

Department of Trade and Industry (Consumer Safety Unit, CA Division)
Electricity Association
Society of British Gas Industries
Co-opted members

This British Standard, having
been prepared under the
direction of the Engineering
Sector Board, was published
under the authority of the
Standards Board and
comes into effect on
15 April 1996
© BSI 08-1999
The following BSI references
relate to the work on this
standard:
Committee reference GSE/29
Draft for comment 92/71976 DC
ISBN 0 580 25367 8

Amendments issued since publication
Amd. No.

Date

Comments


BS EN 625:1996

Contents
Committees responsible
National foreword
Foreword
Text of EN 625
List of references

© BSI 08-1999

Page
Inside front cover
ii
2
5
Inside back cover

i


BS EN 625:1996

National foreword
This British Standard has been prepared under the direction of the Engineering
Sector Board and is the English language version of EN 625:1995 Gas-fired
central heating boilers — Specific requirements for the domestic hot water
operation of combination boilers of nominal heat input not exceeding 70 kW,
published by the European Committee for Standardization (CEN).
EN 625 was produced as the result of international discussion in which the UK
took an active part.

There has previously been no direct British Standard equivalent to this standard.
It is assumed that the execution of the provisions of this document is entrusted to
suitably qualified and experienced persons.
Cross-references
Publication referred to

Corresponding British Standard

EN 297:1994

BS EN 297:1994 Gas-fired central heating boilers —
Type B11 and B11BS boilers fitted with atmospheric
burners of nominal heat input not exceeding 70 kW.

EN 437:1994

BS EN 437:1994 Specification for test gases, test
pressures and categories of appliance, for gas
appliances

A British Standard does not purport to include all the necessary provisions of a
contract. Users of British Standards are responsible for their correct application.
Compliance with a British Standard does not of itself confer immunity
from legal obligations.

Summary of pages
This document comprises a front cover, an inside front cover, pages i and ii,
the EN title page, pages 2 to 16, an inside back cover and a back cover.
This standard has been updated (see copyright date) and may have had
amendments incorporated. This will be indicated in the amendment table on the

inside front cover.
ii

© BSI 08-1999


EUROPEAN STANDARD

EN 625

NORME EUROPÉENNE
September 1995

EUROPÄISCHE NORM
ICS 27.060.30; 91.140.10; 91.140.60

Descriptors: Heaters, gas appliances, central heating, water production, boilers, burners, definitions, equipment specifications,
performance evaluation, tests, safety, energy, consumption, operating requirements, marking, name plates,
classifications

English version

Gas-fired central heating boilers — Specific requirements
for the domestic hot water operation of combination
boilers of nominal heat input not exceeding 70 kW
Chaudières de chauffage central utilisant les
combustible gazeux — Exigences spécifiques à
la fonction eau chaude sanitaire des
chaudières à deux services dont le débit
calorifique nominal est inférieur ou égal

à 70 kW

Heizkessel für gasförmige Brennstoffe —
Spezielle Anforderungen an die
Trinkwasserseitige Funktion von
Kombi-Kesseln mit einer Nennwärmebelastung
kleiner als oder gleich 70 kW

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This European Standard was approved by CEN on 1995-03-06. CEN members
are bound to comply with the CEN/CENELEC Internal Regulations which
stipulate the conditions for giving this European Standard the status of a
national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any
CEN member.
This European Standard exists in three official versions (English, French,
German). A version in any other language made by translation under the
responsibility of a CEN member into its own language and notified to the
Central Secretariat has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium,
Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,
Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and
United Kingdom.

CEN
European Committee for Standardization
Comité Européen de Normalisation
Europäisches Komitee für Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels
© 1995 All rights of reproduction and communication in any form and by any means reserved in all
countries to CEN and its members.
Ref. No. EN 625:1995 E


EN 625:1995

Foreword
This European Standard was prepared by Technical
Committee CEN/TC 109, Central heating boilers
using gaseous fuels, of which the secretariat is held
by NNI.
Other types of boiler including boilers of higher
nominal heat input which are excluded from this
European Standard are dealt with in separate
standards.
This European Standard has been prepared under a
mandate granted to CEN by the European
Commission and the European Free Trade
Association, and supports the essential
requirements of the EU Directive.
In particular, matters which relate to quality
assurance systems, production tests and the
certification of auxiliary controls are not dealt with
in this standard.
In respect of potential adverse effects on the quality
of water intended for human consumption, caused
by the product covered by this standard:
1) This standard provides no information as to

whether the product may be used without
restriction in any of the member states of the EU
or EFTA.
2) It should be noted that, while awaiting the
adoption of verifiable European criteria, existing
national regulations concerning the use and/or
the characteristics of this product remain in force.
In compliance with the common rules of
CEN/CENELEC, the following countries are bound
to apply this European Standard: Austria, Belgium,
Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Netherlands,
Norway, Portugal, Spain, Sweden, Switzerland and
United Kingdom.
For relationship with EU Directives,
see informative Annex ZA, which is an integral part
of this standard.
This European Standard shall be given the status of
a national standard, either by publication of an
identical text or by endorsement, at the latest by
March 1996, and conflicting national standards
shall be withdrawn at the latest by March 1996.

2

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© BSI 08-1999

EN 625:1995

Contents
Foreword
1
Scope
2
Normative references
3
Definitions
3.1
Combination boiler
3.2
“Summer” operating mode
3.3
Specific rate
3.4
Nominal domestic hot water
heat input
3.5
Maximum water service pressure
3.6
Tank
3.7
Thermal store
3.8
Temperature relief valve
3.9
Proportional control of the
domestic hot water operation

3.10 Thermostatic control of the
domestic hot water operation
3.11 Temperature holding thermostat
4
Constructional requirements
4.1
Materials and method of construction
of components of the domestic
water circuit
4.2
Domestic water connections
4.3
Soundness of the domestic
water circuit
4.4
Adjusting, control and safety devices
for the domestic hot water circuit
5
Operational requirements
5.1
General
5.2
Safety of the domestic hot
water circuit
5.2.1 Instantaneous and storage types
5.2.2 Instantaneous type
5.2.3 Storage type
5.3
Rational use of energy
5.3.1 Useful efficiency

5.3.2 Losses
5.4
Fitness for purpose
5.4.1 Instantaneous and storage types —
Specific rate
5.4.2 Instantaneous type
6
Test methods
6.1
General
6.1.1 Adjustment of the domestic
water pressure

Page
2
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6

6.1.2
6.2

Operation of the boiler
Safety of the domestic hot
water circuit
6.2.1 Instantaneous and storage types
6.2.2 Instantaneous type
6.2.3 Storage type
6.3
Rational use of energy
6.3.1 Useful efficiency
6.3.2 Losses
6.4
Fitness for purpose
6.4.1 Instantaneous and storage types —
Specific water rate
6.4.2 Instantaneous type
7
Marking and instructions
7.1
Data plate of the boiler and/or
the tank
7.2
Instructions
7.2.1 Technical instructions for
the installer
7.2.2 Operating instructions for the user
Annex ZA (informative) Clauses of this

European Standard addressing essential
requirements or other provisions
of EU Directives
Figure 1 — Illustration of the test
tank rig [see 6.3.2.1.3 a)]
Table ZA.1
Table ZA.2
Table ZA.3

Page
8
8
8
8
9
9
9
9
11
11
11
12
12
12
12
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6
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6
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13
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blank


EN 625:1995

1 Scope

3 Definitions

This standard supplements standards EN 297,
prEN 483 and prEN 677, hereafter called “boiler
standards”. It specifies the supplementary
requirements and tests for the construction, safety,
rational use of energy, fitness for purpose,
classification and marking related to the domestic
hot water operation of combination boilers.
The domestic hot water is produced by either the
instantaneous or storage principle. The domestic
hot water production is integrated or coupled, and
the whole being marketed as a single unit.
This standard does not apply to two appliances
included in the same case which operate
independently of each other, a boiler and a water
heater, even if they have a common flue.

This standard only covers type testing.

For the purposes of this standard the following
definitions apply.

2 Normative references
This European Standard incorporates by dated or
undated reference, provisions from other
publications. These normative references are cited
at the appropriate places in the text and the
publications are listed hereafter. For the dated
references, subsequent amendments to or revisions
of any of these publications apply to this standard
only when incorporated in it by amendment or
revision. For undated references, the latest edition
of the publication referred to applies.
EN 297:1994, Gas-fired central heating boilers —
Type B11 and B11BS boilers fitted with atmospheric
burners of nominal heat input not exceeding 70 kW.
EN 297/prA2, Gas-fired central heating boilers —
Type B11 and B11BS boilers fitted with atmospheric
burners of nominal heat input not exceeding 70 kW
(determination of efficiency).
EN 437, Test gases — Test pressures —
Appliance categories.
prEN 483, Gas-fired central heating boilers with
atmospheric burners — Type C boilers of nominal
heat input not exceeding 70 kW.
prEN 677, Gas-fired central heating boilers —
Specific requirements for condensing boilers with

nominal heat input not exceeding 70 kW.
ISO 7-1, Pipe threads where pressure-tight joints are
made on the threads — Part 1: Designation,
dimensions and tolerances.
ISO 228-1, Pipe threads where pressure-tight joints
are not made on the threads — Part 1: Designation,
dimensions and tolerances.
ISO 274, Copper tubes of circular section —
Dimensions.

3.1
combination boiler
boiler designed both for central heating and for the
production of domestic hot water. Depending on its
type of domestic hot water production, the
combination boiler is classed as follows, in
accordance with the manufacturer’s declaration
— instantaneous type
Combination boilers which can continuously
supply the specific domestic hot water rate D
stated by the manufacturer.
— storage type
Combination boilers which can intermittently
supply the specific domestic hot water rate D
stated by the manufacturer.
3.2
“summer” operating mode
operating mode in which the boiler only provides
heating of the domestic water

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© BSI 08-1999

3.3
specific rate

the domestic hot water rate declared by the
manufacturer, corresponding to a mean
temperature rise of 30 K, that the boiler can supply
in two successive delivery periods
Symbol: D;
Unit: litres per minute (l/min).
3.4
nominal domestic hot water heat input

the value of the heat input in the domestic hot water
mode indicated by the manufacturer
Symbol: Qnw;
Unit: kilowatt (kW).
3.5
maximum water service pressure
the maximum pressure permitted in the domestic
water circuit, as declared by the manufacturer
Symbol: PMW;
Unit: bar.
3.6
tank
reservoir of domestic water
3.7

thermal store
heat reservoir sited mainly in heating water, as
opposed to the domestic hot water storage in the
tank
5


EN 625:1995

3.8
temperature relief valve
a valve that opens automatically at a given
temperature of maximum 100 °C to discharge the
domestic hot water
3.9
proportional control of the domestic hot water
operation
means of control in which the gas rate is
subordinated proportionally to the domestic hot
water rate; the proportioning factor may be
adjustable
3.10
thermostatic control of the domestic hot water
operation
means of control in which the gas rate is
subordinated to a thermostatic device controlling
the domestic hot water temperature, the set point of
the device may be adjustable
3.11
temperature holding thermostat

a device which maintains the water in the tank or
the thermal store at a given temperature

4 Constructional requirements
It is checked that the assembly meets constructional
requirements by visual examination of the boiler
and possibly the tank, and also by inspection of the
technical file.
4.1 Materials and method of construction of
components of the domestic water circuit
Materials shall be appropriate for their use, under
intended application and at the maximum water
pressure stated by the manufacturer.
The requirements relating to thermal insulation
and its use specified in the “boiler standards” only
apply to parts of the domestic water circuit likely to
come into contact with flames or sited close to the
combustion products outlet.
The materials of the parts containing domestic
water shall not affect the quality of the domestic
water in respect of either health or taste.
The whole of the domestic hot water circuit shall be
made up of corrosion resistant materials or shall be
protected against corrosion.
4.2 Domestic water connections
Threaded connections shall comply with ISO 228-1
or ISO 7-1.
If copper tubes are used for the connection, the end
of the tube shall comply with ISO 274.

6

In accordance with the manufacturer’s instructions,
the domestic water circuit shall be able to be
drained, without the discharge of water
compromising electrical safety.
4.3 Soundness of the domestic water circuit
The domestic hot water circuit and the heating
circuit shall be separate. If an actuator or a control
has a sliding shaft or a link with the diaphragm
separating:
— the gas circuit and the heating water circuit;
— the heating water circuit and the domestic
water circuit;
— the gas circuit and the domestic water circuit;
there shall be an air vent between these circuits.
The area of this aperture shall be at least 19 mm2
and it shall be possible to introduce a 3,5 mm pin
gauge into it.
4.4 Adjusting, control and safety devices for
the domestic hot water circuit
If necessary, the domestic hot water circuit shall be
protected with control and safety devices to comply
with the requirements, “Thermostats and water
temperature limiting devices — General” of
clause 2 of EN 297 and clause 5 of prEN 483.
The tank shall be fitted with a device for controlling
the water temperature. This device shall allow a
temperature to be attained which is sufficient to
prevent the build up of bacteria (see 5.2.3.3).

Where circumstances require, and the appliance is
equipped with a temperature relief valve, any device
controlling the temperature of the domestic hot
water shall act before this valve.

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5 Operational requirements
5.1 General
If the nominal heat input in domestic hot water
mode exceeds the nominal heat input in the central
heating mode, the safety requirements of the “boiler
standards” given below are checked at the nominal
heat input in the domestic hot water mode and at
the maximum water temperature:
— soundness of the combustion circuit;
— limiting temperatures;
— ignition, cross lighting and flame stability;
— flame supervision device;
— combustion products discharge safety device
(for type B11BS boilers);
— carbon monoxide.

© BSI 08-1999


EN 625:1995

5.2 Safety of the domestic hot water circuit

5.2.3.3 Temperature of the domestic hot water

5.2.1 Instantaneous and storage types

Under the test conditions of 6.2.3.3, it shall be
possible to adjust to or obtain a domestic hot water
temperature of at least 60 °C in the tank.

5.2.1.1 Soundness of parts containing domestic
water
Under the test conditions of 6.2.1.1, the parts
containing domestic water shall withstand the test
pressure without permanent distortion or
soundness defects, with respect to the outside or the
heating circuit.
5.2.1.2 Overheating of the domestic hot water by the
heating circuit
Under the test conditions of 6.2.1.2, the domestic
hot water temperature shall not exceed 95 °C.
5.2.1.3 Failure of the domestic hot water
temperature control device
Under the test conditions of 6.2.1.3:
— for boilers in which the domestic water circuit
is not in direct contact with the combustion
products, with normal control out of operation
and according to the option chosen, at least the
requirement relating to the limit
thermostat (3.5.7.3.2.1 test no. 1 of EN 297
or 6.5.7.3.2.1 test no. 1 of prEN 483) or the safety
temperature limiter (3.5.7.3.2.2 of EN 297

or 6.5.7.3.2.2 of prEN 483) shall be met.
— for boilers in which the domestic water circuit
comes into total or partial contact with the
combustion products, the domestic water
temperature limiting device shall at least cause
safety shutdown before the tap water reaches a
temperature of 100 °C.
5.2.2 Instantaneous type
5.2.2.1 Maximum domestic hot water temperature
Under the test conditions of 6.2.2.1, the domestic
hot water temperature shall not exceed 95 °C.
5.2.2.2 Overheating of the domestic hot water
Under the test conditions of 6.2.2.2, the domestic
hot water temperature shall not exceed 95 °C.
5.2.3 Storage type
5.2.3.1 Maximum temperature of the domestic hot
water
Under the test conditions of 6.2.3.1, the domestic
hot water temperature shall not exceed 95 °C.
5.2.3.2 Overheating of the domestic hot water
Under the test conditions of 6.2.3.2, for boilers in
which part of the tank is in contact with products of
combustion, the domestic hot water temperature
shall not exceed 95 °C.

© BSI 08-1999

5.3 Rational use of energy
5.3.1 Useful efficiency
The considered useful efficiency is that measured in

the central heating mode.
5.3.2 Losses
The losses of the boiler and the tank (where
applicable) measured under the test conditions
of 6.3.2, shall be less than the value given by the
following formula:
qs = 0,014 V2/3 + 0,02Qnw
where:
qs

are the losses of the boiler and the tank in
kilowatts (kW);

V

is the water capacity of the tank (including
the water in any integral heat exchanger)
and/or the thermal store (if applicable) in
litres (l);

Qnw is the nominal domestic hot water heat
input of the boiler, in kilowatts (kW).
5.4 Fitness for purpose
5.4.1 Instantaneous and storage types —
Specific rate
Under the test conditions of 6.4.1, the measured
value of the specific rate shall not be more than 5 %
below the value D stated by the manufacturer on the
data plate.
5.4.2 Instantaneous type

5.4.2.1 Nominal domestic hot water heat input
Under the test conditions of 6.4.2.1, the nominal
domestic hot water heat input shall be obtained or
may be adjusted to within ± 5 %.
5.4.2.2 Water pressure to obtain the nominal heat
input
Under the test conditions of 6.4.2.2, the heat input
obtained shall be at least 95 % of the heat input
obtained in 6.4.2.1.
5.4.2.3 Obtaining the domestic hot water
temperature
Under the conditions of 6.4.2.3, it shall be possible
to achieve or adjust to, a water rate that corresponds
to a temperature of between 50 °C and 80 °C for
boilers with a thermostatic control or a temperature
rise at the boiler outlet of between 45 K and 65 K for
boilers with proportioning control.

7


EN 625:1995

5.4.2.4 Heating-up time of the domestic hot water
Under the test conditions of 6.4.2.4, the heating-up
time shall not exceed 2 min.

6 Test methods
6.1 General
Unless otherwise specified, the general test

conditions of the “boiler standards” are
supplemented as stated below:
— cold water: (10 ± 2) °C;
— hot water: 50 °C or as near as possible;
— central heating water (if necessary): see “boiler
standards” (flow 80 °C, return 60 °C).
For the tests:
— the domestic water pressure is the difference
between the static inlet and outlet pressures of
the boiler measured as close as possible to the
boiler;
— the inlet and outlet temperatures of the
domestic water are measured in the centre of the
flow and as close as possible to the boiler.
In certain tests, a low inertia thermometer is used.
“Low inertia thermometer” means a measuring
instrument with a response time such that 90 %
of the final temperature rise, in the range 15 °C
to 100 °C, is obtained within 5 s when the sensor is
plunged into still water.
6.1.1 Adjustment of the domestic water
pressure
The domestic water pressure shall be adjusted
to ± 4 % of the required value.
6.1.2 Operation of the boiler
Except where otherwise specified, the tests are
carried out with the boiler operating in the domestic
water mode and the “summer” operating mode.
6.2 Safety of the domestic hot water circuit
6.2.1 Instantaneous and storage types

6.2.1.1 Soundness of the parts containing domestic
water
The domestic water circuit is subjected to a pressure
of 1,5 times the maximum pressure given on the
data plate for 10 min.
It is checked that the requirements of 5.2.1.1 are
met.
6.2.1.2 Overheating of the domestic hot water by the
central heating circuit

The appliance operates continuously for 1 h at the
nominal heat input in the central heating mode,
without drawing domestic hot water. A draw off at
the specific rate D is then carried out and the
requirement of 5.2.1.2 is checked.
6.2.1.3 Failure of the domestic hot water
temperature control device
The requirement of 5.2.1.3 is checked after the
control device of the domestic hot water circuit has
been put out of operation:
— for boilers in which the domestic hot water
circuit does not come into direct contact with the
combustion products, testing is carried out
according to the test methods relating to the
limit thermostat (4.5.7.3.2.1 test no. 1 of EN 297
or 7.5.7.3.2.1 test no. 1 of prEN 483) or the safety
temperature limiter (4.5.7.3.2.2 of EN 297
or 7.5.7.3.2.2 of prEN 483);
— for boilers in which the domestic water circuit
comes into total or partial contact with the

combustion products, the boiler’s hot water
tapping rate is progressively decreased until the
point is reached where the burner is shut off.
Where the boiler is fitted with a range rating device,
the test is carried out at the maximum adjusted heat
input in the central heating mode.
6.2.2 Instantaneous type
6.2.2.1 Maximum temperature of the domestic hot
water
The boiler is supplied with an appropriate reference
gas (EN 437) and is operated at the nominal
domestic hot water heat input with a domestic
water supply pressure of 2 bar.
Starting with this 2 bar supply pressure, the
pressure is progressively reduced until the burners
are extinguished. The water outlet temperature is
measured continuously with a low inertia
thermometer. The maximum temperature is
measured and shall satisfy the requirements
of 5.2.2.1.
6.2.2.2 Overheating of the domestic hot water
The boiler is supplied with an appropriate reference
gas (EN 437) and is operated at the nominal
domestic hot water heat input. The water rate and,
where appropriate, any water temperature control
are adjusted to obtain the maximum water
temperature at the nominal domestic hot water heat
input.

The boiler is supplied with an appropriate reference

gas (EN 437). The central heating circuit thermostat
is set at its maximum position.

8

© BSI 08-1999


EN 625:1995

After the boiler has operated for 10 min, the hot
water delivery tap is turned off quickly. After 10 s
the tap is turned on quickly and the highest
temperature at the centre of the flow, as close as
possible to the boiler outlet, is measured by means
of a low inertia thermometer. The boiler remains in
operation until it has again reached its steady state
condition. The same measurements are made
during similar operating cycles, but with the time
that the draw off is stopped increased each time
by 10 s, until the maximum temperature is
obtained.
It is checked that the requirement of 5.2.2.2 is met.

6.3 Rational use of energy

6.2.3 Storage type

The losses from the boiler/tank assembly are
determined by adding up the losses from the boiler

and the tank.
The manufacturer states how the tank has to be
separated from the boiler, and which pipework has
to be taken into account in the boiler losses and
which will be counted with the tank.

6.2.3.1 Maximum temperature of the domestic hot
water
The boiler is supplied with an appropriate reference
gas (EN 437) and is operated at the nominal
domestic hot water heat input with the domestic
water thermostat at its maximum position. A draw
off is carried out after a shut down of the burner.
The maximum temperature measured shall meet
the requirement of 5.2.3.1.
6.2.3.2 Overheating of the domestic hot water
The test commences after the tank or the thermal
store has reached temperature and after the burner
has been shut down a second time by the controls.
Water is drawn off several times at a rate
corresponding to 5 % of the water capacity of the
tank, in litres per minute.
On each occasion, water is drawn until the burner
ignites and at least 95 % of the nominal domestic
hot water heat input is obtained. The next draw off
then takes place immediately after the burner shuts
down, and so on until the maximum temperature is
obtained.
For modulating burners or burners with several
rates, the next drawing takes place when the gas

rate has decreased at least to 50 % of the maximum
domestic hot water heat input reached.
As each draw off commences, the temperature of the
delivered water is measured and it is checked that
the requirement of 5.2.3.2 is met.

6.3.1 Useful efficiency
The test is carried out in the central heating mode
in the “boiler standards”.
6.3.2 Losses
Depending on the way in which hot water is
produced, the requirement of 5.3.2 is checked under
the test conditions defined below.
6.3.2.1 Tank which can be disconnected from the
boiler
6.3.2.1.1 General

6.3.2.1.2 Boiler
For the boiler, the losses (standby losses) are
measured as in amendment EN 297/pr A2.
The exchanger for the tank is disconnected from the
boiler.
Also, where the boiler and the tank are coupled
within the same case, the losses from the boiler
alone are measured with the tank empty.
6.3.2.1.3 Tank
For the tank, the following mode of operation is
used:
If the tank and the boiler are coupled within the
same case, the losses from the tank alone are

determined with the boiler empty.
a) Preliminary conditions
The test is carried out with a rig equivalent to
that described in Figure 1, in a room where the
ambient temperature is between 15 °C
and 25 °C, with a permitted temperature
variation of ± 5 °C during the test.
The installation includes an electrical resistance
and a circulating pump (long circuit of Figure 1).

6.2.3.3 Temperature of the domestic hot water
Where applicable, the adjuster is placed in the
position stated by the manufacturer. After a
controlled shutdown of the boiler, a draw off is
carried out for 10 min at a rate equivalent to 5 % of
the water capacity of the tank per minute or at the
minimum rate stated by the manufacturer which
allows burner ignition if this is greater than 5 % of
the capacity of the tank per minute. After 1 min, it
is checked that the requirements of 5.2.3.3 are met.

© BSI 08-1999

9


EN 625:1995

Before the test is carried out, the tank is placed
in the position recommended by the

manufacturer. For a tank with two positions,
vertical or horizontal, the test is done in the
vertical position. It is filled with water heated to
a temperature of (65 ± 2) °C by circulation in a
closed circuit, in which the tank and its
exchanger are arranged in series. The tank
domestic water temperatures are deemed to
have reached uniformity at the time t1 that
circulation stops, if the following conditions are
met:
— the difference between the domestic water
outlet temperature (Ts) and the domestic
water inlet temperature (Te) remains less
than 1 K continuously for 15 min before
time t1;
— the inlet temperature (Te) has not changed
by more than 1 K during this period.
It is assumed that the mean water temperature
(To) of the tank at moment t1 is equal to the
arithmetic mean of the inlet and outlet
temperatures at that moment:
Te + T
T o = --------------------s2
The preliminary conditions are met if this
temperature To is equal to (65 ± 2) °C.
b) Cooling of the tank and determination of
the corrected final mean temperature (Tfc)
At t1, valves 2 and 3 shown in Figure 1 are shut
off, and all the water connections are
disconnected and sealed at valves 2 and 3.

The parts of the pipework external to the tank
shall be carefully insulated so that the heat
losses attributable to them are negligible
compared to the losses from the tank.
The tank is left to cool for a measured time
of 24 h ± 20 min (t2). The ambient temperature is
measured at least every hour and the arithmetic
mean (Tamb) calculated.
The final mean water temperature (Tf) of the
tank at time t2 is determined by the following
method;
— the connections of the short circuit of
Figure 1 are remade and the circulating pump
is put into operation;
— the mean water temperature of the tank at
time t2 is that obtained after stabilization
when the temperature difference between the
inlet and outlet is less than 1 K. The
re-circulation time is taken into account in the
cooling time;

10

— the corrected final mean water temperature
(Tfc) of the tank is calculated by taking account
of the water mass and water temperature of
the test rig short circuit. This connecting
circuit will be designed such that the
correction to the final temperature is less
than 0,5 K for a tank of capacity exceeding 50 l

and 1 K for a tank of capacity not
exceeding 50 l.
The corrected final mean water temperature
(Tfc) of the tank is calculated as follows:
(V × Tfc) + (Vb × Ta) = (V + Vb) × Tf
whence:

where:
Tfc

is the corrected final mean water
temperature in degrees Celsius (°C);

Tf

is the mean water temperature of the tank
measured at time t2 in degrees Celsius (°C);

Ta

is the ambient temperature at time t2 in
degrees Celsius (°C) (assuming that at the
end of 24 h the short circuit is at ambient
temperature);

V

is the water capacity of the tank (including
the water in any integral heat exchanger), in
litres (l). This value is declared by the

manufacturer and checked from the
drawings;

Vb

is the volume of water in the connecting short
circuit of the test rig, in litres (l).
c) Calculation of the losses of the tank
The value of the losses of the tank is given by the
following relationship:

or

© BSI 08-1999


EN 625:1995

where
qa45

are the losses of the tank for a
temperature rise of 45 K, in kilowatts
(kW);

After a waiting time of 20 min after the end of the
first drawing, a new water drawing is carried out
for 10 min and the temperature and water rate are
recorded.
For each drawing the following is calculated:

t2 – t1 is the period of cooling, in hours (h);
To

is the mean water temperature of the
tank at time t1, in degrees Celsius (°C);

Tfc

is the corrected mean water temperature
of the tank at time t2, in degrees Celsius
(°C);

Tamb

is the mean ambient temperature during
cooling, in degrees Celsius (°C);

V

is the water capacity of the tank
(including the water in any integral heat
exchanger), in litres (l). This value is
declared by the manufacturer and
checked from the drawings.

6.3.2.2 Tank or thermal store which is integral with
and cannot be separated from the boiler
The losses for the boiler tank or the boiler thermal
store assembly are determined as stated for the

boiler alone in amendment EN 297/pr A2, or for a
difference between the temperature declared by the
manufacturer in 6.4.1 and the ambient temperature
if this difference is greater than 45 K.
For this test, the tank and its exchanger (if
appropriate) are connected in series with the boiler.
6.4 Fitness for purpose
6.4.1 Instantaneous and storage types —
Specific rate
The boiler is supplied with an appropriate reference
gas (EN 437) at the nominal domestic hot water
heat input with an inlet water pressure of 2 bar.
The domestic hot water temperature is adjusted,
where possible, to obtain an average temperature
rise as close as possible to 30 K which permits the
nominal domestic hot water heat input to be
obtained.
Before the test, the boiler is in the “summer”
operating mode, at thermal equilibrium, without
any draw off.
For storage type boilers, the setting of the domestic
hot water thermostat is adjusted to 65 °C or the
value stated by the manufacturer for boilers with
integral, non-removable tanks. If by design,
the 65 °C temperature cannot be achieved, the test
is carried out at the closest possible temperature
to 65 °C. The first drawing is carried out no earlier
than the second controlled shut down of the burner
and lasts 10 min. The temperature and the water
rate are recorded.

© BSI 08-1999

where
Di

is the specific rate D1 and D2,
determined respectively during the first
and second draw offs, in litres per
minute (l/min);

mi(10)

is the quantity of water collected during
the first or second draw off, in litres (l);

%t

is the mean effective temperature rise of
the collected water, in kelvin (K).

If the difference between D1 and D2 does not
exceed 10 % of their average value, the requirement
applies to:
D 1 + D2
----------------------2
If the difference between D1 and D2 exceeds 10 % of
their average value, the requirement applies to the
lowest value of the two.
It is checked that the requirements of 5.4.1 are met.
6.4.2 Instantaneous type

6.4.2.1 Nominal domestic hot water heat input
The test is carried out with each appropriate
reference gas (EN 437) at a water pressure of 2 bar.
The gas rate may be adjusted in accordance with the
manufacturer’s instructions. A water draw off is
carried out to check that the requirement of 5.4.2.1
is satisfied.
6.4.2.2 Water pressure to obtain the nominal
domestic hot water heat input
The test is carried out by lowering the water
pressure to the minimum value stated by the
manufacturer and it is checked that the
requirement of 5.4.2.2 is satisfied.
6.4.2.3 Obtaining the domestic hot water
temperature
The boiler is adjusted as stated in 6.1 and 6.4.2.1
with an appropriate reference gas (EN 437). Then
draw offs are carried out at water pressures
of 2, 3, 4 and 6 bar or at the water pressures
declared by the manufacturer if they are less than
these values.
The domestic hot water rate is adjusted in
accordance with the technical instructions (7.2.1)
and the information on the data plate (7.1.1).
11


EN 625:1995

In the steady state, it is checked that the

requirement of 5.4.2.3 is met for the maximum and
minimum positions of the central heating
thermostat if it is adjustable.
6.4.2.4 Heating-up time of the domestic hot water
The boiler is adjusted in accordance with 6.1
and 6.4.2.1 with an appropriate reference gas
(EN 437).
The central heating thermostat and/or the
temperature holding thermostat for the domestic
hot water, if it exists, is set to the minimum
temperature position.
The water rate and the means of temperature
adjustment (if it is adjustable) are adjusted to
obtain the following water temperature conditions
at the nominal domestic hot water heat input and in
the steady state:
— boilers with fixed output or proportioning
control: a temperature rise of 45 K;
— boilers with thermostatic control: an outlet
temperature of 50 °C.
Then the boiler is put into thermal equilibrium
without any drawing off.
When thermal equilibrium is achieved, or at the end
of a control cycle, if it exists, the drawing tap is
opened.
The flow time is measured from the opening of the
tap until 90 % of the temperature rise or the water
outlet temperature stated above is attained.
These temperatures are measured with a low
inertia thermometer. It is checked that the

requirement of 5.4.2.4 is met.

7 Marking and instructions
7.1 Data plate of the boiler and/or the tank

7.2 Instructions
7.2.1 Technical instructions for the installer
The technical instructions for the installer specified
in the “boiler standards” shall be supplemented as
follows:
— for all types of boilers:
— the information given on the data plate as
specified in 7.1;
— the mass rate, in grams per second (g/s), and
the average temperature of the combustion
products in the domestic water mode, in degrees
Celsius (°C), (measured under the conditions
of 6.4.1);
— for storage type combination boilers:
— where necessary, describe how the boiler and
the tank are connected;
— indicate that it will be necessary to fit safety
devices specified in local installation regulations,
if they have not been fitted on the boiler by the
manufacturer;
— for instantaneous type combination boilers;
— the minimum pressure at the inlet to the
domestic water circuit.
7.2.2 Operating instructions for the user
Operation instructions for the user specified in the

“boiler standards” shall be supplemented by
information necessary for normal domestic hot
water operation.
In particular, they shall state:
— the temperature in the tank or the thermal
store necessary to obtain the claimed specific
water rate;
— the precautions to be taken in case of freezing.

The data from the “boiler standards” on the data
plate shall be supplemented by the following
information for combination boilers:
— nominal heat input in the domestic hot water
mode (Qnw), in kilowatts (kW), if there are
different nominal heat inputs for the central
heating and domestic water modes;
— maximum water service pressure for the
domestic water circuit (P.MW), in bars;
— value of the specific water rate, D, (either on
the boiler or on the tank), to the first decimal
place, in litres per minute (l/min).

12

© BSI 08-1999


EN 625:1995

Figure 1 — Illustration of the test tank rig [see 6.3.2.1.3 a)]

© BSI 08-1999

13


EN 625:1995

Annex ZA (informative)
Clauses of this European Standard
addressing essential requirements or
other provisions of EU Directives
This European Standard has been prepared under a
mandate given to CEN, by the European
Commission and the European Free Trade
Asociation and supports essential requirements of
EU Directive.
WARNING: other requirements and other EU
Directives may be applicable to the products falling
within the scope of this standard.
The following clauses of this standard are likely to
support requirements of Directive 90/396/EEC “Gas
appliances”.
Compliance with these clauses of this standard
provides one means of conforming with the specific
essential requirements of the Directive concerned
and associated EFTA regulations.

14

© BSI 08-1999


EN 625:1995

Table ZA.1
Essential
requirements

Object

Clauses and/or paragraphs in
the standard which comply
wholly or in part with the
essential requirement

1

Annex I of the Directive — general conditions

1.1

Safety of operation

4.4 to 5.1 and 5.2.3.3

1.2

Marking and instructions
Installation instructions

Operating instructions for the user
Warnings on the appliance and on the packaging
Official languages

7.2
7.2.1
7.2.2
EN*
EN*

1.2.1

Information in the installation instructions
Gas type
Supply pressure
Combustion air rate
Discharge of combustion products

EN*
EN*
EN*
EN*

1.2.2

Contents of the operating instructions for the user

EN* and 7.2.2

1.2.3

Warning on the appliance and packaging

EN*

1.3

Equipment

EN*

2

Materials

2.1

Characteristics

EN* and 4.1

2.2

Guarantee

EN*

3

Design and construction

3.1
3.1.1

General
Resistance to contraints

EN* and 4.1

3.1.2

Condensation

EN*

3.1.3

Risk of explosion

EN*

3.1.4

Water penetration

4.3

3.1.5

Normal fluctuation of auxiliary energy

EN* and 5.2

3.1.6

Abnormal fluctuation of auxiliary energy

EN* and 5.2

3.1.7

Hazards of electrical origin

EN*

3.1.8

Pressurised parts

EN* and 5.2.1.1

3.1.9

Failure of safety devices:
— flame supervision device;
— combustion products discharge safety device
(type B11BS);
— automatic burner control systems;
— overheat protection;
— gas circuit.

EN*
EN*
EN*, 4.4 and 5.2.1.3
EN*, 4.4, 5.2.1.2 and 5.2.1.3
EN*

3.1.10

Safety/adjustment

EN*

3.1.11

Protection of parts set by the manufacturer

EN*

3.1.12

Marking of taps, adjusting or control devices

EN*

3.2
3.2.1

Unburnt gas release
Risk of gas leakage

EN*

3.2.2

Risk of gas accumulation in the appliance

EN*

3.2.3

Risk of gas accumulation in the rooms

EN*

© BSI 08-1999

15


EN 625:1995

Table ZA.1
Essential
requirements

Object

Clauses and/or paragraphs in
the standard which comply

wholly or in part with the
essential requirement

3.3

Ignition:
— ignition and re-ignition;
— cross-lighting.

3.4
3.4.1

Combustion
Flame stability
Concentration of substances harmful to health in the
combustion products

EN*
EN*

3.4.2

Release of combustion products

EN*

3.4.3

Release of combustion products into the room for appliances
connected to a flue

EN*
(type B11BS) under abnormal draught conditions

3.4.4

CO limit in the room (independent flueless heating
appliances and flueless intantaneous water heaters)

Not applicable

3.5

Rational use of energy

EN* and 5.3

3.6
3.6.1

Temperatures
Floor and adjacent walls

EN*

3.6.2

Knobs

EN*

3.6.3

Temperature of external surfaces

EN*

3.7

Foodstuffs and water used for sanitary purposes

Foreword and 4.1

NOTE

EN*
EN*

EN* not specific to the domestic hot water operation and already covered in the “boiler standards”

Table ZA.2
Certification
of conformity

Object

1

Annex II of the Directive
NOTE

Clauses and/or paragraphs in
the standard which comply
wholly or in part with the
requirement

EN* not specific to the domestic hot water operation and already covered in the “boiler standards”

Table ZA.3
EC mark and
inscriptions

Object

Clauses and/or paragraphs in
the standard which comply
wholly or in part with the
requirement

Annex III of the Directive
1

CE mark

EN*

2

Appliance or its data plate:
— CE mark;
— manufacturer’s name or identification symbol;

— trade name;
— electrical supply;
— appliance category;
— installation information.

EN*
EN*
EN*
EN*
EN*
7.1

NOTE

16

EN* not specific to the domestic hot water operation and already covered in the “boiler standards”

© BSI 08-1999