157292-3.pmd

Concord CXSD/H -

Installation & Servicing

GENERAL

Boiler

CXSD 40/H

CXSD 50/H

CXSD 60/H

CXSD 70/H

CXSD 80/H

CXSD 90/H CXSD 100/H

CXSD 110/H

CXSD 120/H

Number of sections

Flow tappings

Rc (in. BSP)

2 x 2 at rear

Return tappings

Rc (in. BSP)

2 x 2 at rear

Maximum static head

metres (feet)

61.0 (200)

45.7 (150)

Maximum pressure

bar (p.s.i.)

6.0 (87)

Gas inlet connection

Rc (in. BSP)

3/4 (3/4)

1 (1 )

Min. dynamic gas

mbar gauge

15.5

16.5

15.0

16.0

17.5

16.0

17.5

pressure required at boiler inlet in.w.g.

6.2

6.6

6.0

6.4

7.0

6.4

7.0

Electricity supply

230 Volts- single phase, 50 Hz, fuse 5 A

Nominal flue size (to BS. 835)

m m

150

175

200

250

in.

Diverter outlet socket

m m

184

213

238

288

internal diameter

in.

7.3

8.4

9.4

11.2

Length of burner bars (overall)

m m

377

497

617

737

837

14.8

19.5

24.3

29.0

33.7

Main burner injectors (3 off)

size, mm

3.4

3.82

4.12

4.57

4.86

5.2

5.3

5.5

5.6

Approximate dry weight

210

265

330

395

490

lb.

463

584

727

871

1078

Water content

litre

gal.

4.8

6.6

8.2

9.9

11.5

Table 3 - Boiler Control specification Maximum Flow temperature 85

Table 2 - General Data

Electricity supply

230V, 50Hz, fuse 5A

Ignition

5 attempts followed by non-volatile lockout.

Gas valve

High/Low and Off

Gas safety time

Maximum of 10 secs with 5 attempts with one min. between attempts.

Safety check

The control de-energises every 4 hours to check internal control functions.

Pump

Pump overrun operates if the flow temperature is greater than 75

Boiler thermostat

The boiler thermostat hysteresis is a maximum of 3

Table 1- Performance Data

Boiler

CXSD 40/H

CXSD 50/H

CXSD 60/H

CXSD 70/H

CXSD 80/H

CXSD 90/H

CXSD 100/H

CXSD 110/H

CXSD 120/H

Boiler Input

Gross

33.8

42.2

50.7

59.1

67.6

76.0

84.5

92.9

101.3

Low Rate

Btu/hr x 1000 115.3

144.1

172.9

201.7

230.5

259.3

288.2

317.0

345.8

Nett

30.4

38.0

45.7

53.3

60.9

68.5

76.1

83.7

91.3

Btu/hr x 1000 103.8

129.8

155.8

181.7

207.7

233.6

259.6

285.6

311.5

Boiler Input

Gross

48.3

60.3

72.4

84.5

96.5

108.6

120.7

132.7

144.8

High Rate

Btu/hr x 1000 164.7

205.8

247.0

288.2

329.3

370.5

411.7

452.8

494.0

Nett

43.5

54.3

65.2

76.1

87.0

97.8

108.7

119.6

130.4

Btu/hr x 1000 148.3

185.4

222.5

259.6

296.7

333.8

370.9

408.0

445.0

Boiler output

100

110

120

High Rate

Btu/hr x 1000 136.5

170.6

204.7

238.8

273.0

307.1

341.2

375.3

409.4

Gas rate

High

4.60

5.75

6.90

8.05

9.20

10.35

11.50

12.64

13.79

/h 162.4

203.0

243.6

284.2

324.8

365.4

406.0

446.6

487.1

Approx. flue

4.5% CO

&100°C.m

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

gas volume

4.5% CO

& 212°F. ft.

106

127

148

170

191

212

233

254

Manifold setting pressure

mbar

9.7

9.8

10.2

10.0

9.3

9.6

10.7

11.1

12.1

High

in.w.g.

3.9

4.1

4.0

3.7

3.8

4.3

4.4

4.8

Manifold setting pressure

mbar

4.8

5.0

4.9

4.6

4.7

5.2

5.4

5.9

Low

in.w.g.

1.9

2.0

1.8

1.9

2.1

2.2

2.4

Part load efficiency (Gross)

81.9

81.6

82.7

82.0

82.5

83.2

83.4

82.4

Seasonal efficiency (SEDBUK)*

[80.4]% [80.3]% [80.4]% [80.4]% [80.4]% [80.4]% [80.4]% [80.4]% [80.4]%

* This value is in the UK government's Standard Assessment Procedure (SAP) for energy rating of dwellings.
The test data from which it has been calculated has been certified by Advantica 0087.

Note. To obtain gas consumption in l/s, divide gross heat input (kW) by a calorific value of 37.8 (MJ/m

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Concord CXSD/H -

Installation & Servicing

GENERAL

CAUTION.

To avoid the possibility of injury during the installation, servicing or cleaning of

this appliance, care should be taken when handling edges of sheet steel components.

CONTENTS

Air Supply. ......................................................................... 8

Boiler Assembly - exploded view. .................................... 9

Boiler Clearances. ............................................................ 5

Burner Assemblies - exploded views. ..............................

CXSD 40/H-90/H. ........................................................ 26
CXSD 100/H-120/H ..................................................... 27

Casing Assembly. ........................................................... 12

Chimney System. .............................................................. 8

Commissioning. .............................................................. 17

Controls. ............................................................................ 4

Electrical Connections. .................................................. 14

Electrical Supply. .............................................................. 8

Fault Finding. ................................................................... 32

Gas Safety Regulations .................................................... 3

Gas Supply. ........................................................................ 8

Hydraulic Resistance. ...................................................... 5

Initial Lighting. ................................................................. 17

Installation. ........................................................................ 9

Mandatory Requirements. ............................................... 7

Option Kits. ........................................................................ 4

Pump. ................................................................................ 6

Servicing. ........................................................................ 24

Short List of Parts. ......................................................... 35

Site Assembled Boilers. ................................................. 30

Static Head Requirements. .............................................. 6

System Connections. ..................................................... 11

Ventilation. ........................................................................ 8

Water Circulation. ............................................................ 4

Water Connections. ......................................................... 4

Water Treatment. ............................................................. 6

Wiring Diagrams. ............................................................ 15

Concord CXSD 40/H - 120/H (Natural gas) B.G. Certified - P.I. No. 87/AQ/103

Destination Countries: GB & IE

INTRODUCTION
CONSTRUCTION

Boiler body
The sectional boiler body is of cast iron and is supplied assembled
on a sheet steel combustion chamber with an integral draught
diverter. The boiler can be supplied in sectioned form to special
order for site assembly - refer to the section headed `Instructions
for Site Assembled Boilers'.

Casing
The casing is manufactured in stove enamelled sheet steel and
is easily assembled on site.

Burners
The 3 burners are of stainless steel construction.

Current Gas Safety (Installation and Use)
Regulations or rules in force.

It is the law that all gas appliances are installed and serviced by
a CORGI registered installer in accordance with the above
regulations. Failure to install appliances correctly could lead to
prosecution. It is in your own interest, and that of safety, to ensure
that the law is complied with.

The Concord CXSD 40/H-120/H range of boilers has been tested
and certified by British Gas to prEN656 for use with Natural gas
only.

Multiple boiler installations

The Concord CXSD/H range is certificated for use in multiple
boiler installations, providing that the following conditions are
satisfied.

1. A downdraught thermostat kit MUST be fitted to ALL boilers

in the installation.

2. A maximum of 6 boilers may be used with a single flue

header.

3. For clearances see Frame 2.

A comprehensive guide to multiple installations of Concord
CXSD/H boilers is available.

WARNING. Failure to use a downdraught kit on every boiler in
a multiple boiler installation will negate the certification of the
installation and therefore contravene the essential requirements
of the Gas Appliance Directive.

Note. The CXSD 40/H, CXSD 50/H and CXSD 60/H boilers are
intended for use as commercial boilers and are NOT certified for
use in domestic applications. A domestic installation is defined
as an installation where the boiler takes its combustion air from
a living space or from a room directly or indirectly connected with
the living space. It is important, therefore, that no external control
devices - e.g. flue dampers, economisers etc., are directly
connected to this appliance unless covered by these Installation
and Servicing Instructions or otherwise recommended by
Caradon Ideal Limited in writing. If in doubt please enquire.
Any direct connection of a control device not approved by Caradon
Ideal Limited could invalidate the British Gas Certification, the
normal appliance warranty and could also infringe the Gas Safety
Regulations. Table 1, Table 2 and the descriptive notes which
follow contain all the essential data likely to be required by the
installer.

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Concord CXSD/H -

Installation & Servicing

GENERAL

Flow and return connections are 2" BSP.

A 1" BSP tapping is provided in the redundant return flange for
the cold feed or expansion vessel connection.

Safety Valve
A safety valve must be sized and fitted in accordance with BS.
6644 for every type of system. The valve should be set at 0.7
bar (10 lb/in.

) above the operating pressure in the boiler. The

maximum safety valve setting is 0.7 bar (10 lb/in.

) above the

maximum design operating pressure of 6 bar (87 lb/in.

Cold Feed/Open Vent
The independent cold feed and the open vent must comply
with BS. 6644 and be of the following minimum size.

Boiler Size

Cold Feed

Open Vent

CXSD 40/H - 50/H

3/4

CXSD 60/H-120/H

1/4

Sealed system filling point - refer to Frame 8

WATER CONNECTIONS

GAS CONTROLS

The gas controls consist of a high / low arrangement with
direct burner ignition.

ELECTRICAL CONTROLS

WARNING. THE ON/STANDBY [1/0] button does NOT electrically
isolate the boiler.

The CXSD/H incorporates an advanced microprocessor based
control system which operates all electrical functions of the boiler
including ignition, flame detection, thermostatic control, and high/
low operation. In addition, the microprocessor has onboard
servicing and commissioning instructions and a fault diagnosis
programme.
The illuminated LED display gives a continual read-out of the boiler
status and functions, but in the unlikely event of a fault condition
will display the fault areas.

OPTION KITS

Pressure Gauge Kit
A pressure gauge is available for the range of boilers. Details
for fitting are included with the pressure gauge.

Downdraught thermostat
This kit is optional when used on a single CXSD/H installation,
but mandatory when used on a multiple boiler installation.

Remote Indication Board (volt free)
This provides the ability for remote indication of lockout and
overheat conditions.

Outside Sensor
This kit provides a sensor for temperature compensation when
the outside temperature changes

DUTY

The range of boilers is suitable for: Combined indirect pumped
domestic hot water and central heating systems; Independent
indirect pumped domestic hot water or central heating systems.

Fully pumped systems may be open vented or sealed.

The range of boilers is NOT suitable for:

1. Gravity DHW systems.
2. Gravity heating systems.
3. Direct domestic hot water supply.

WATER CIRCULATION SYSTEM

Due to the compact nature of the boiler the heat stored within the
castings at the point of shutdown of the burner must be dissipated
into the water circuit in order to avoid the overheat thermostat
tripping. In order to allow pump operation after burner shutdown
the boiler control box incorporates a pump overrun facility which
operates when the boiler switches off and until the flow temperature
is below 75

C and, in order to make use of this, the pump must be

wired to the appropriate terminal L

(pump) in the boiler control

box.
1. The minimum flow rate as given in Table 5 must be maintained

whenever the boiler is firing and during the pump overrun
period.

2. During the period of pump overrun there must be an open

circuit of adequate water volume and/or load. The minimum
size of this circuit is given by the use of Graph 1.
Examples shown on Graph 1

a. For the CXSD 90/H and CXSD 100/H the minimum circuit

during pump overrun could be a load of 6 kW with a volume
of 31 litres or any other combination given by the relevant
line.

b. For the CXSD 70/H and CXSD 80/H the minimum circuit

during pump overrun could be a load of 2 kW with a volume
of 45 litres or any other combination given by the relevant
line.

The above circuit capacity during pump overrun may be
achieved either by provision of an adequate bypass circuit or
by ensuring that a zone of suitable size is open for circulation
during this period by relevant control of zone valves or pumps.

continued on page 6

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Concord CXSD/H -

Installation & Servicing

GENERAL

CLEARANCES & DIMENSIONS

Boiler Size

CXSD 40/H CXSD 50/H CXSD 60/H CXSD 70/H CXSD 80/H CXSD 90/H CXSD 100/H CXSD 110/H CXSD 120/H

Front clearance

mm (in)

750 (29

1/2

)

Rear clearance

mm (in)

150 (6)

300 (12) 300 (12) 300 (12) 300 (12)

Side clearance

mm (in)

50 (2)

100 (4)

Dimension A

m m

750

882

1042

1212

1385

1/2

3/4

1/2

Dimension B

m m

108

122

135

190

160

1/4

7/8

3/8

1/2

1/4

Dimension C

m m

931

893

5/8

3/16

Dimension D

m m

177

187

224

271

321

3/8

7/8

5/8

Dimension E

m m

116

163

213

3/4

1/8

5/8

1/2

3/8

Table 4

POSITION OF BOILER

Minimum clearances required
from walls or other fixed objects
to allow for the free access of
combustion air are shown in
Table 4 above.
However, for maintenance
purposes we suggest a
minimum rear clearance of
50mm.
Any combustible material
adjacent to the boiler and its flue
system must be so placed or
shielded as to ensure that its
temperature does not exceed 65

C (150

F).

MULTIPLE BOILER INSTALLATIONS

The minimum installation clearances must
conform to the dimensions given below:

CXSD 40/H, 50/H, 60/H, 70/H & 80/H

Clearance between boilers = 50mm
Clearance at both ends of the multiple installation = 50mm*

CXSD 90/H, 100/H, 110/H & 120/H

Clearance between boilers = 100mm
Clearance at both ends of the multiple installation = 100mm*
Rear clearance: sufficient clearance should be given at the
rear of the boiler for connection of gas and water pipework.
*Additional clearance is required for access at either end of
the installation.

100

CON5214

Example A

Example B

CXSD 1

10/H &

CXSD 120/H

CXSD 100/H & CXSD 90

CXSD 80/H & CXSD 70/H

CXSD 40/H

CXSD 60/H & CXSD 50/H

Heat Load During Pump Overrun (kW)

Water Volume in Circuit during Pump Overrun (litres)

Relationship between load and water volume for the

minimum capacity of water circuit during the 6 minute

pump overrun period for different boiler outputs.

Graph 1 - Heat Load / Water Volume

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

190 200

160 170 180

120

110

100

90
80
70
60
50
40
30
20
10

Graph 2 - Hydraulic Resistance

Hydraulic

Resistance

(mbar)

Flow (litres/min)

C(20

-
CXSD

40/H

C(20

-
CXSD

50/H

C(20

-
CXSD

60/H

C(20

-
CXSD

70/H

C(20

-
CXSD

80/H

C(20

-
CXSD

90/H

C(20

-
CXSD

100/H

C(20

-
CXSD

1
10/H

C(20

-
CXSD

120/H

403-1

CON5215

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Concord CXSD/H -

Installation & Servicing

GENERAL

Particular reference should be made to BS. 6644: Section 2;
Subsection 10 and Guidance note PM5 "Automatically controlled
steam and hot water boilers" published by the Health and Safety
Executive.

The information and guidance given below is not intended to override
any requirements of either of the above publications or the
requirements of the local authority, gas or water undertakings.

Other British Standards applicable are BS.5422 & BS.6700.

The information provided is based on the following assumptions:

1. An independent open vent/safety pipe connection is made to

the redundant boiler flow tapping or is positioned immediately
after the system flow pipe connection to the header, as shown.

2. An independent cold feed/expansion pipe connection is made

to the redundant boiler return tapping. Cold feed/expansion pipe
connections made to the pumped system return will result in an
increase in the static head requirement, caused by the additional
resistance of the distributor tube. Surging may also increase.

3. The maximum flow rate through the boiler is based on a

temperature difference of 11°C at full boiler output and the
circulating pump is positioned in the flow to the system.

4. The boiler is at the highest point of circulation in the system.

Systems designed to rise above the boiler flow tappings will
automatically require a minimum static head higher than that
shown.

5. The position of the open vent/safety pipe above the expansion

cistern water level is given as a guide only. The final position will
depend upon the particular characteristics of the system.
Pumping over of water into the expansion cistern must be
avoided.

Note A.
This minimum height must be increased, if
necessary, to comply with the minimum head
required by the pump manufacturer in order to
avoid cavitation.
Note B.
This diagram does not show safety valves, water
flow switches, etc., necessary for the safe
operation of the system.

PUMP POSITIONS

Whenever practically possible the circulating pump(s) should be
positioned so that it pressurises the system being served. The
vertical distance between the pump(s) and any cold feed and
expansion cistern MUST comply with the pump manufacturers
requirements in order to avoid cavitation. These requirements
override the information given in Frame 3 if the static head
required for the pump(s) exceeds that required for the boiler.

MINIMUM FLOW OF WATER - Refer to Table 5

The system design must provide for an adequate flow rate
through the boiler at all times when the boiler is firing. The
minimum flow rate should correspond to a temperature
difference across the boiler flow and return of 35

C (63

F),

assessed at catalogue rating.

WATER TREATMENT FOR HOT WATER AND
HEATING BOILERS

There is a basic need to treat the water contained in all heating
and indirect water systems, particularly open vented systems. It is
assumed, incorrectly, that because boilers are operating in
conjunction with what is apparently a closed circuit an open vented
system will not, under normal circumstances, allow damage or
loss of efficiency due to hardness salts and corrosion once the
initial charge of water has been heated up a few times.

1mm of lime reduces the heat transfer from metal to water by
10%.

In practice the deposition of these salts is liable to cause noises
from the boiler body or even premature boiler failure. Corrosion
and the formation of black iron oxide sludge will ultimately result
in premature radiator failure.

Open vented systems are not completely sealed from the
atmosphere if proper venting and expansion of system water is to
be achieved. The same tank is used to fill the system with water
and it is through the cold feed pipe that system water expands
into the tank when the boiler passes heat into the system.

Table 5 - Flow rates for fully pumped systems

Boiler

Minimum flow rates for a

temperature difference of 35

C (63

l/s

g.p.m.

CXSD 40/H

0.28

3.7

CXSD 50/H

0.34

4.5

CXSD 60/H

0.41

5.4

CXSD 70/H

0.48

6.3

CXSD 80/H

0.55

7.3

CXSD 90/H

0.62

8.2

CXSD 100/H

0.68

CXSD 110/H

0.75

9.9

CXSD 120/H

0.82

10.9

3 OPEN VENTED SYSTEMS - Minimum static head requirements

The wiring diagrams in Frames 16,17 &18 illustrate the control
methods for achieving the above.

3. Pump selection should take account of the hydraulic resistance

given in Graph 2.

CON5349

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Concord CXSD/H -

Installation & Servicing

GENERAL

SEALED (PRESSURISED) SYSTEMS

Working pressure 6 bar maximum.

Particular reference should be made to BS. 6644: Section 6
Guidance note PM5 "Automatically controlled steam and hot
water boilers" published by the Health and Safety Executive.

The information and guidance given below is not intended to
override any requirements of either of the above publications or
the requirements of the local authority, gas or water undertakings.

In general, commercial closed pressurised systems are provided
with either manual or automatic water make up.

On both instances it will be necessary to fit automatic controls
intended to protect the boiler, circulating system and ancillary
equipment by shutting down the boiler plant if a potentially
hazardous situation should arise.

Examples of such situations are low water level and operating
pressure or excessive pressure within the system. Depending
on circumstances, controls will need to be either manual or

automatic reset. In the event of shutdown both visual and
audible alarms may be necessary.

Pressure vessels used must comply with BS. 4814 and must
be sized on the basis of the total system volume and initial
charge pressure.

Initial minimum charge pressure should not be less than 0.5
bar (7.2 psi) and must take account of static head and
specification of the pressurising equipment. The maximum
water temperatures permissible at the point of minimum
pressure in the system are specified in Guidance Note PM5.

When make up water is not provided automatically it will be
necessary to fit controls which shut down the plant in the event
of the maximum system pressure approaching to within 0.35
bar (5 psi) of safety valve setting.

Other British Standards applicable to commercial sealed
systems are:-

BS. 6880: Part 2.
BS. 1212
BS. 6281: Part 1
BS. 6282: Part 1
BS. 6283: Part 4

FOR SMALL PIPE INSTALLATIONS;
BS. 6891;

Installation of low pressure pipework

FOR LARGE PIPE INSTALLATIONS

Gas Installations
IGE-UP-1:

Purging Procedures of Non-domestic Gas
Installations. Soundness Testing Procedures
for Industrial and Commercial.

IGE-UP-2:

Guidance notes on the Installation of Gas
Pipework, Boosters and Compressors in
Customer's Premises Equal to or Greater
than 25mm (Non-domestic).

IGE-UP-10:

Installation of Gas Appliances in Industrial and
Commercial Premises.

BS.6644:

Installation of Gas Fired Hot Water Boilers
70kW to 1.8MW (net).

BS 6880 Pt 1-3: Water Supply.
CP342:2:

Centralised Hot Water Supply.

Model Water Bye-laws
Manufacturers notes must not be taken, in any way, as
overriding statutory obligations.

The appliance must be installed in a room separated from living
rooms and provided with appropriate ventilation direct to the outside
- see Table 6.

FOUNDATION

The boiler must stand on a non-combustible floor (i.e. concrete or
brick) which must be flat, level and of a suitable load bearing
capacity to support the weight of the boiler (when filled with water)
and any ancillary equipment.

If the boiler is mounted on a plinth then the dimensions must exceed
the plan area of the boiler by at least 75mm on each side.

Conversely, when the system cools, water previously expelled is
drawn back from the tank into the system together with a quantity
of dissolved oxygen.

Even if leakage from the heating and hot water system is
eliminated there will be evaporation losses from the surface of
the tank which, depending upon ambient temperature, may be
high enough to evaporate a large portion of the system water
capacity over a full heating season.

There will always be corrosion within a heating or hot water system
to a greater or lesser degree, irrespective of water characteristics,
unless the initial fill water from the mains is treated. Even the
water in closed systems will promote corrosion unless treated.
For the reason stated, Caradon Ideal Limited strongly recommend
that when necessary the system is thoroughly cleaned, prior to
the use of stable inhibitor, which does not require continual
topping up to combat the effects of hardness salts and corrosion
on the heat exchangers of the boiler and associated systems.

Caradon Ideal Limited advise contact directly with specialists
on water treatment such as:

Fernox Manufacturing Co. Ltd., or Sentinel Division,
Tandem House,

Betz Dearborn Ltd.,

Marlowe Way,

Widnes,

Croydon,

Cheshire, WA8 8UD

Surrey CRO 4XS

Tel. 0151 424 5351

Tel. 0870 601 5000

INSTALLATION REQUIREMENTS

The appliance must be installed by a CORGI registered installer.

The installation of the boiler must be in accordance with the
relevant requirements of the Gas Safety Regulations, current
I.E.E. (BS. 7671) Regulations, Model Water Bye-laws, local
water authority bye-laws and it should also comply with any
relevant requirements of the local gas supplier, local authority
and the relevant British Standard Codes of practice and
building regulations.

These appliances are NOT suitable for installation where they
will be exposed to the elements. A boiler room shall be
constructed or adapted to meet the requirements of BS 6644.
The maximum ambient temperature is 32

C at 1.5 metres from

the floor with a maximum humidity of 90% RH.

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Concord CXSD/H -

Installation & Servicing

GENERAL

Position ventilation grilles to avoid the risk of accidental
obstruction by blockage or flooding. If further guidance on
ventilation is required then consult BS.6644 or BS.5440:2:2000

AIR SUPPLY BY MECHANICAL VENTILATION

The supply of air by mechanical means to a space housing the
boiler should be by mechanical inlet with natural or mechanical
extraction. Mechanical extract ventilation with natural inlet must
not be used.

Where a mechanical inlet and a mechanical extract system is
applied, the design ventilation flow rates should be as in Table 4
of BS.6644.

The requirements for air supply by mechanical ventilation are given
in BS.6644.

Note. For mechanical ventilation systems an automatic control
should be provided to cause safety shutdown or lockout of the
boiler(s) in the event of failure of air flow in either inlet or extract
fans.

IMPORTANT. The use of an extractor fan in the same room as the
boiler (or in an adjacent, communicating room) can, in certain
conditions, adversely affect the safe operation of the boiler. Where
such a fan is already fitted (or if it is intended to fit an extractor fan
after installation of the appliance) the advice of the gas supplier
should be obtained.

Tests for spillage of products from the draught diverter when the
extractor fan is running and all doors and windows are shut should
be carried out after installation, If spillage is detected, the area of
permanent ventilation must be increased.

CHIMNEY SYSTEM

To ensure the safe and satisfactory operation of the boiler then
the chimney system (which may be common or individual, in the
case of twin or multiple boiler inst