Alpha Alpha CD25C User guide

Installation and Servicing
Instructions
Alpha CD25C/28C/35C
Range of Wall Mounted, Fan Assisted, Room Sealed,
Gas Fired, High Efficiency Condensing Combination Boilers
Alpha CD25C G.C. No. 47 532 31
Alpha CD28C G.C. No. 47 532 33
Alpha CD35C G.C. No. 47 532 35
British Gas
Service Listed
For use with Natural Gas only
Leave these instructions with the User
Nepicar House, London Road,
Wrotham Heath, Sevenoaks,
Kent TN15 7RS
For Technical help or for Service call ...
ALPHAHELPLINE
Tel: [phone]
0051

2Alpha CD25C/28C/35C - Contents/Introduction
CONTENTS
1 Introduction ....................................... 2
2 Technical data................................... 3
3 General boiler information.................. 7
4 Installation......................................... 13
5 Commissioning ................................. 19
6 Boileroperation ................................. 22
7 Routineservicing............................... 23
8 Component replacement ................... 25
9 Wiring diagrams ................................ 31
10 Fault finding ...................................... 33
11 Short parts list ................................... 37
12 Benchmark Checklist ........................ 38
13 Service record ................................... 39
The Alpha CD range of high efficiency condensing boilers are wall mounted, fan assisted room-sealed combination boilers.
The burner is lit electronically and the heat output is controlled by a modulating fan and gas valve.
The CD25C, CD28C and CD35C are combination boilers providing both central heating and domestic hot water at mains
pressure.
The boilers are supplied with a pump, pressure relief valve, expansion vessel and pressure gauge fully assembled and tested.
They are designed for use with a fully pumped, sealed and pressurised central heating system using only Natural gas.
The CD25C boiler is suitable for central heating loads of between 5.5 and 19.5 kW (18 766 and 66 550 Btu/h).
The CD28C boiler is suitable for central heating loads of between 6.3 and 25.9 kw (21 496 and 88 400 Btu/h).
The CD35C boiler is suitable for central heating loads of between 7.8 and 30.3 kw (26 614 and 103 400 Btu/h).
The maximum output available for domestic hot water is 24.3 kW (84 800 Btu/h), capable of providing 9.6 litres/min for the Alpha
CD25Cboiler,28.7kW(97900Btu/h),providing11.4litres/min fortheAlphaCD28C boiler and34.6kW(118100Btu/h),providing
14.2 litres/min for the Alpha CD35C boiler, all with a temperature rise of 35°C.
IMPORTANT
It is the law that all gas appliances are installed by a competent person, ie CORGI registered personnel, in accordance with
the following recommendations:-
Current Gas Safety (Installation and Use) Regulations
All current Building Regulations issued by the Department of the Environment, i.e. Approved Document L1.
Building Standards (Scotland) (Consolidation) Regulations issued by the Scottish Development Department
UK Water Regulations/Byelaws (Scotland)
Health & Safety Document No. 635 (The Electricity At Work Regulations 1989)
The installation should also be in accordance with the following British Standard Codes of Practice:-
BS 5440:1:2000 Flues
BS 5449:1990 Forced circulation hot water systems
BS 5546:2000 Installation of hot water supplies for domestic purposes
BS 6700:1997 Design, installation, testing and maintenance of services supplying water
BS 6798:2000 Installation of gas fired hot water boilers
BS 6891:1998 Gas installation
BS 7593:1992 Code of Practice for treatment of water in heating systems
BS 7671:2001 Requirements for electrical installations, IEE Wiring Regulations
Reference should be made to DEFRA document 'Guide to condensing boiler installation assessment procedures for dwellings'.
If installation is in a timber framed building, refer to the Institute of Gas Engineers document IGE/UP/7.
This appliance meets the requirements of IPX4D, ie degree of protection against moisture.
Failure to install this appliance correctly could lead to prosecution. It is in your own interest and that of safety to ensure that the
law is complied with.
Manufacturer's instructions must NOT be taken in anyway as over-riding statutory obligations.
Notes: 1. Ensure that the Benchmark Checklist has been completed after the boiler has been installed and commissioned.
2. It is the law that all boiler installations are registered by the installer through the CORGI Gas Work Notification
Scheme.
3. The boiler must only be used with Alpha CD condensing flue components.
1 INTRODUCTION

3
2.1 PERFORMANCE - NATURAL GAS (CAT: I2H 2H - G20 - 20 mbar)
2 TECHNICALDATA
Alpha CD25C/28C/35C - Technical Data
Alpha CD25C
MAX.
20.4
69 600
18.4
62 780
19.5
66 550
18.0
61 420
2.82
1.13
1.94
68.5
MIN.
6.4
21 960
5.8
19 780
6.1
20 820
5.5
18 780
0.40
0.16
0.61
21.5
Room sealed
chamber panel
fitted
Central Heating
Heat Input (Hs)kW
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Heat Output (Hscondensing) kW
(50°C/30°C) Btu/h
Heat Output (Hinon-condensing) kW
(80°C/60°C) Btu/h
Differential Burner mbar
Pressure in wg
Gas Rate m³/h
ft³/h 9.6
2.2
11.2
2.5
MAX.
26.7
91 100
24.1
82 200
24.3
84 800
5.49
2.20
2.55
90.0
MIN.
6.4
21 960
5.8
19 780
5.5
18 780
0.40
0.16
0.61
21.5
Domestic Hot Water
Heat Input (Hs)kW
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Output to Water (Hs)kW
(modulating) Btu/h
Differential Burner mbar
Pressure in wg
Gas Rate m³/h
ft³/h
Flow Rate at 35°C Rise L/min
gal/min
Specific Flow Rate (D) at 30°C Rise L/min
(Flow rate @ 30K to EN625) gal/min
Room sealed
chamber panel
fitted
Alpha CD25C
MAX.
27.1
92 400
24.4
83 250
25.9
88 400
24.0
81 900
5.73
2.29
2.59
91.4
MIN.
7.3
24 900
6.6
21 500
6.9
23 500
6.3
21 500
0.52
0.21
0.70
24.7
Room sealed
chamber panel
fitted
Central Heating
Heat Input (Hs)kW
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Heat Output (Hs condensing) kW
(50°C/30°C) Btu/h
Heat Output (Hi non-condensing) kW
(80°C/60°C) Btu/h
Differential Burner mbar
Pressure in wg
Gas Rate m³/h
ft³/h
Alpha CD28C
11.4
2.5
13.3
2.9
Domestic Hot Water
Heat Input (Hs)kW
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Output to Water (Hs)kW
(modulating) Btu/h
Differential Burner mbar
Pressure in wg
Gas Rate m³/h
ft³/h
Flow Rate at 35°C Rise L/min
gal/min
Specific Flow Rate (D) at 30°C Rise L/min
(Flow rate @ 30K to EN625) gal/min
Room sealed
chamber panel
fitted
Alpha CD28C
MIN.
7.3
24 900
6.6
22 500
6.3
21 500
0.52
0.21
0.70
24.7
MAX.
31.6
107 900
28.5
97 200
28.7
97 900
7.47
2.98
3.02
106.6
MAX.
31.6
107 800
28.5
97 200
30.3
103 400
28.0
95 550
2.01
0.80
3.02
106.6
MIN.
8.9
30 600
8.1
27 600
8.5
29 000
7.8
26 600
0.25
0.10
0.86
30.4
Room sealed
chamber panel
fitted
Central Heating
Heat Input (Hs)kW
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Heat Output (Hs condensing) kW
(50°C/30°C) Btu/h
Heat Output (Hi non-condensing) kW
(80°C/60°C) Btu/h
Differential Burner mbar
Pressure in wg
Gas Rate m³/h
ft³/h
Alpha CD35C
14.2
3.13
15.6
3.44
Domestic Hot Water
Heat Input (Hs)kW
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Output to Water (Hs)kW
(modulating) Btu/h
Differential Burner mbar
Pressure in wg
Gas Rate m³/h
ft³/h
Flow Rate at 35°C Rise L/min
gal/min
Specific Flow Rate (D) at 30°C Rise L/min
(Flow rate @ 30K to EN625) gal/min
Room sealed
chamber panel
fitted
Alpha CD35C
MIN.
8.9
30 600
8.1
27 600
8.0
27 300
0.25
0.10
0.86
30.4
MAX.
38.0
129 600
34.3
117 000
34.6
118 100
3.07
1.23
3.64
128.5
Note: The above appliances are fully modulating and are not range rated.

4
720 mm
440 mm
300 mm
340 mm
22 mm
2.5 L
2.8 L
3.2 L
100 mm
60 mm
Case Dimensions Height
Width
Depth
Depth (with Jig)
Gas Connection
Primary Water Content CD25C
CD28C
CD35C
Air Duct Diameter
Flue Duct Diameter
2.6 GENERAL
Min. Clearances for Servicing Top
(from casing) Bottom
Sides
Front
Flue Terminal Size
Flue Terminal Protruding
Hole Size Required For Flue Assy.
Lift Weight CD25C
CD28C
CD35C
2.5 INSTALLATION
235 mm
250 mm
5 mm
450 mm
100 mm Dia.
100 mm
110 mm Dia.
43 kg
44 kg
45 kg
Central Heating (Sealed System)
Max. Working System Pressure
Min. System Pressure
Max. System temperature
Pressure Relief Valve Setting
Expansion Vessel Size (pre-charge press.)
Flow Connection
Return Connection
Relief Valve Connection
Recommended System Pressure (cold)
CH Water Temp. (Approx. max.)
2.5 bar
0.5 bar
82°C
3 bar (44 PSI)
8 L at 0.8 bar
22 mm
22 mm
15 mm
1.0 bar
82°C (180°F)
Domestic Hot Water
Max. Mains Inlet Water Pressure
Min. Mains Water Pressure
Min. DHW Flow Rate
Mains Inlet Connection
DHW Outlet Connection
DHW Water Content CD25C
CD28C
CD35C
Outlet Water Temp. (Approx. max.)
8 bar
0.2 bar
2.5 l/min
15 mm
15 mm
0.2 L
0.26 L
0.32 L
62°C (144°F)
2.2 SYSTEM
Burner
Main Heat exchanger
DHW Heat Exchanger
Main Burner Injector CD25C
CD28C
CD35C
Flue - Outer Duct
Flue - Inner Duct
Stainless steel
Stainless steel
Stainless Steel
5.2 mm
5.4 mm
8.5 mm
White
Plastic
2.3 COMPONENTS 2.4 ELECTRICAL
Supply
External Fuse
Power Consumption
Internal Fuse
Electrode Spark Gap
ElectricalEnclosureDegreeofMoistureProtection
230/240 V ~ 50 Hz
3 A
130 W
F2 A
3 - 4 mm
IPX4D
Alpha CD25C/28C/35C - Technical Data
2.7 PERFORMANCE
Band 'A'
5
SEDBUK Rating
NOx Classification
Boiler Model
CD25C
CD28C
CD35C
%CO2content (± 0.2%)
Natural Gas
Min.
9.0
9.1
9.0
CH Max.
9.4
9.3
9.3
DHW Max.
9.4
9.3
9.3

5
Alpha CD25C/28C/35C - Technical Data
Fig. 1
2.8 FLUE LENGTHS
CD Easy-Flue 500 mm with terminal and 90° bend. A CD Easy-Flue 1000 mm with terminal and 90° bend is also available.
CD 750 mm and 1000 mm flue extensions are available.
Length of Flue Required:-
Rear Flue = wall thickness + 140 mm (includes terminal). This is without back frame, add 40 mm if the wall jig is used.
Side Flue = wall thickness + distance between wall and side of boiler + 225 mm (includes terminal)
Vertical Flue = distance from top of boiler side panel to required roof position minus 1 m for vertical terminal assembly
Maximum horizontal flue length = 12 m.
Maximum vertical flue length including terminal is 15 m.
Each additional CD 90° Bend is equivalent to 1.3 m of flue length.
Each CD 45° Bend is equivalent to 0.9 m of flue length.
The CD Vertical Flue terminal assembly is equivalent to 1 m of flue length.
2.9 AVAILABLE PUMP HEAD FOR CENTRAL HEATING
gal/min
3.7
2.8
2.3
1.8
0.7
Btu/h
86 700
64 000
53 000
42 200
18 100
kW
25.40
18.70
15.60
12.35
5.30
Output (50/30°C) Available pump head
metres
2.3
3.5
3.8
4.0
4.6
feet
7.6
11.6
12.6
13.2
15.2
litre/min
16.6
12.6
10.5
8.3
3.2
20°C 20°C
Flow rate
This information is based on 20°C system design temperature difference.
Note: For outputs upto 28 kW refer to Section 3.7.
2.10 ELECTRICAL CONNECTIONS
Note: This Appliance Must Be Earthed
An optional integral single channel Clock kit is available if required.
Note: Only use the Alpha single channel clock. Do not fit any two channel clocks.
Boiler terminal block
Clock connections
1. Ensure wires are connected
correctly
2. Only fit the Alpha recommended
single channel clock. Other
clocks could cause damage.
WARNING
Blue
Wire
Brown
Wire
Red
Wire
12345Internal Clock Terminals
Red
Wire
Not
Used

6
2.11 BOILER SCHEMATIC
1 - Seasonality valve
2 - DHW flow switch and filter
3 - Diverter valve
4 - Gas valve
5 - Primary temperature sensor
6 - DHW heat exchanger
7 - Main burner
8 - Primary/condensing heat exchanger
9 - Room sealed chamber
10 - Fan
11 - Pressure differential test points
12 - Flue hood
Fig. 2
13 - Overheat thermostat
14 - Expansion vessel
15 - Automatic air vent
16 - Pump
17 - Drain point
18 - Pressure relief valve
19 - Primary pressure switch
20 - Ignition electrodes
21 - Flame sensing electrode
22 - DHW temperature sensor
23 - Flue sampling point
24 - Gas service cock
25 - Mains inlet on/off valve
26 - On/off valve (2 off)
27 - Automatic by-pass
28 - Cyclone separator (if applicable)
29 - Condensate trap
30 - Injector
31 - Venturi
32 - Venturi negative point
33 - Venturi positive point
34 - Flue thermostat
35 - Diverter valve motor
Alpha CD25C/28C/35C - Technical Data
Gas
Condensate
discharge
Primary
Heating
return Primary
Heating
flow
24
4
23
-
-
+
+
9
10
29
35
11
34
5
13
20
14
32
33
15
16
17
18
27
28
26
Domestic
hot water
outlet
Cold mains
water inlet
1
2
3
6
19
22
25
12
8
721
31
30

7
3.1 GAS SUPPLY
The Alpha CD25C boiler requires a gas rate of 2.55 m³/h (90.1 ft³/h).
The Alpha CD28C boiler requires a gas rate of 3.02 m³/h (106.7 ft³/h).
The Alpha CD35C boiler requires a gas rate of 3.64 m³/h (128.5 ft³/h).
The meter and supply pipes must be capable of delivering this quantity of gas in addition to the demand from any other
appliances in the house. The boiler requires at least a 22 mm gas supply pipe.
The complete installation, including the meter, must be tested for gas soundness and purged as described in BS 6891.
3.2 ELECTRICAL SUPPLY
The boiler requires a 230/240 V ~ 50 Hz mains supply, fused at 3 A
The boiler must be earthed.
There must only be one common isolator, providing complete electrical isolation, for the boiler and any external controls.
This boiler has been fitted with a supply cable, however, if it is necessary to fit a cable use PVC insulated cable not less than
0.75 mm² (24 x 0.2 mm) to BS 6500 Table 16. The boiler should be connected to a fused three pin plug and unswitched
shuttered socket outlet (both complying with BS 1363), or a fused double pole switch with a contact separation of at least 3 mm
in both poles.
Wiring external to the boiler must be in accordance with the current IEE Wiring Regulations (BS 7671).
Note: If a room thermostat is fitted, it must be suitable for 230/240 V switching.
3.3 AIR SUPPLY
The boiler does not require any air vents for cooling in the room in which it is installed or when installed in a cupboard or
compartment. The minimum clearances for servicing must always be maintained.
Note: A cupboard or compartment used to enclose the boiler must be designed and constructed specifically for the purpose,
i.e. comply with the Building Regulations.
3.4 FLUE SYSTEM - Fig. 3
The flue system must be installed in accordance with BS 5440:1.
For horizontal flues ensure the Easy Flue assembly is horizontal and the inner duct is sloping downwards towards the boiler.
When additional flue extensions are used, ensure the flue slopes downwards towards the boiler by a minimum of 25 - 30 mm
per metre of flue.
Flue components are available as follows:-
CD Easy-Flue 500 mm (includes 90° bend and terminal) - Part No. 6.2000500.
CD Easy-Flue 1000 mm (includes 90° bend and terminal) - Part No. 6.2001000.
CD 750 mm flue extension - Part No. 6.2000750.
CD 1000 mm flue extension - Part No. 6.2001050
CD 90° bend - Part No. 6.2000590.
CD 45° bend - Part No. 6.2000545.
CD Vertical flue terminal assembly. Refer to the separate installation instructions supplied with the assembly.
The following methods determine the correct length of flue required.
For rear exit flue (including terminal) L = B + 140 mm (180 mm if wall jig is used)
For side exit flue (including terminal) L = B + C + 225 mm (min. side clearance required is 5 mm)
For vertical flue L = H minus 1000 mm for vertical terminal assembly
Where L = Required flue length
B = Finished wall thickness
C = Distance from the inside wall to the side of the boiler
H = Distance from top of boiler side panel to roof position
Note: 1. If an extra 90° bend is used, this reduces the maximum flue length by 1.3 m. Each 45° bend used reduces the maximum
flue length by 0.9 m.
2. Under no circumstances must the flue length (including allowances for extra bends) exceed 12 metres horizontally and
only 15 metres vertically.
3. Failure to use Alpha CD flue components with the boiler will invalidate the boilers CE approval, guarantee and may be
unsafe.
3 GENERAL BOILER INFORMATION
Alpha CD25C/28C/35C - General Boiler Information

8
HORIZONTAL FLUE OPTIONS - Lmax = 12 metres
L = B + C + E + 225 mm
Alpha CD25C/28C/35C - General Boiler Information
L = B + C + 225 mm
CB
E
CB
E
B
F
B
C
L = B + E + F + 225 mm + (90° bend = 1.3 metre)
(add 40 mm to 'F' if a jig is used)
L = B + C + 225 mm + (2 x 45° bends = 1.8 metre)
Fig. 3
VERTICAL FLUE OPTIONS
Not less than
300 mm
Not less than
300 mm
H
Hmax=15m
Not less than
300 mm
Not less than
300 mm
H
Hmax = 13.2 m

9
3.5 FLUE TERMINAL LOCATION - Fig. 4
Note: In certain weather conditions the terminal will emit a plume of steam. If possible avoid positioning the terminal where this may
cause a nuisance, i.e. positions A, D, G, H, J or M.
The flue terminal must be exposed to the external air and the position must allow the free passage of air across it at all times.
A terminal must not be sited below 2.1 m where people have access to, such as public footpaths, access routes, patios etc.
However, If the terminal is fitted less than 2.1 m above a surface where there is no public access, the terminal must be
protected by a terminal guard. A suitable guard is available from Alpha Therm Ltd.
3.6 BOILER LOCATION
The boiler is not suitable for external installation unless it is installed within a purpose designed weatherproof building.
The boiler must be installed on a flat vertical wall which is capable of supporting the weight of the boiler. The boiler can be fitted
to or adjacent to a wall comprising of a combustible material without the need for a special thermal insulation barrier.
If the boiler is to be fitted in a timber framed building, it should be fitted in accordance with the Institute of Gas Engineers 'Guide
for Gas Installations in Timber Frame Housing', reference IGE/UP/7.
The boiler may be installed in any room or internal space, although particular attention is drawn to the requirements of the
current IEE Wiring (BS7671) Regulations, and in Scotland, the electrical provisions of the Building Regulations applicable in
Scotland, with respect to the installation of the boiler in a room or internal space containing a bath or shower. Where a room-
sealed boiler is installed in a room containing a bath or shower, it must not be possible for a person using the bath or shower
to touch any electrical switch or boiler control utilising mains electricity.
The boiler may be installed in a cupboard or compartment, provided it is correctly designed for that purpose, i.e. complies with
the Building Regulations and the requirements of BS 6798.
Alpha CD25C/28C/35C - General Boiler Information
Notes: 1.In addition, the terminal should not be nearer
than 150 mm to the framework of an
opening into the buiding, i.e. a window
surround or door surround.
2.This clearance may be reduced to 25 mm
without effecting the performance of the
boiler. However, to ensure the condensate
plume does not affect adjacent surfaces a
clearance of 300 mm is preferable.
3.These clearances may be reduced to 25 mm
withouteffectingtheperformanceoftheboiler.
However, to ensure the condensate plume
does not affect adjacent surfaces the terminal
canbeextendedbeyondgutters,pipes,eaves,
balconies etc. by upto 500 mm. If the flue is
extended more than 500 mm outside, it should
be boxed and insulated.
4.To reduce the possibility of nuisance to
neighbouring buildings etc. it is
recommended the terminal shouild not be
less than 2500 mm from car parking spaces,
building boundary walls, fences etc.
Note: A terminal must not be sited under a car port roof
A Directly below an opening, air brick, windows, etc.
B Below gutters, soil pipes or drain pipes
C Below eaves
D Below balconies
E From a vertical drain pipe or soil pipe
F From an internal or external corner
G Above ground, roof or balcony level
H From a surface or boundary facing the terminal
I From a terminal facing the terminal
J Above an opening, air brick, window etc.
K Vertically from a terminal on the same wall
L Horizontally from a terminal on the same wall
M Horizontally from an opening, air brick, window etc.
N Minimum protrusion through a roof
O From a vertical obstruction
P From an openable window
Q From an adjacent vertical terminal
Min. distance (mm)Terminal position 300 (See Note 1)
75 (See Note 3)
200 (See Note 3)
200 (See Note 3)
150 (See Note 3)
300 (See Note 2)
300
600 (See Note 4)
1200 mm
300 (See Note 1)
1500 mm
300 mm
300 mm (See Note 1)
300 mm
300 mm
600 mm
600 mm
J
D
G
HI
Q
Boundary
OP
N
Fig. 4

10
3.7 CENTRAL HEATING SYSTEM - Fig. 5
The boiler is designed for use in a sealed central heating system in accordance with the requirements of BS 5449 and BS 6798.
The system should be designed to operate with flow temperatures of up to 82°C. When designing the system, the pump head, expansion
vessel size, mean radiator temperature, etc. must all be taken into account. Refer to the pump performance table for guidelines.
System volume - The expansion vessel incorporated into the boiler is suitable for a sealed heating system with a maximum
water content of 80 litres (18 gal). Above 80 litres, consideration should be given to fitting an additional expansion vessel fitted
in the position shown in Fig. 5. To check correct operation of the expansion vessel(s) the system pressure should not be more
than 2.5 bar when the system is at maximum operating temperature (for further guidance refer to BS 7074:1).
The boiler is supplied with the following components built in:-
Pressure relief valve - complying with BS 6759 and set to operate at 3 bar. The discharge pipe must be routed clear of the
boiler and terminated in such a manner that it can be seen, but cannot cause injury to persons or property.
Pressure gauge - To indicate the system pressure to be maintained.
Expansion vessel - Conforming to BS 4814 with a capacity of 8 litres and pre-charged to a pressure of 0.8 bar.
By-pass - The boiler incorporates an automatic by-pass, therefore an automatic by-pass is not required for the system.
Cyclone - This is a device fitted in the heating return within the optional wall jig to remove any foreign or solid matter etc. from
the system.
Alpha CD25C/28C/35C - General Boiler Information
3.8 FILLING THE CENTRAL HEATING SYSTEM - Figs. 6, 7
Thesystem designpressure(cold)shouldbesetto1.0bar.This pressureisequivalent toastatic head(seeFig. 5)of10.2 metresofwater.
Provision should be made to replace water lost from the system. This can be by manual or automatic means, as shown in Figs.
6 and 7. The position for connecting an automatic make-up vessel is indicated in Fig. 5. A double check valve assembly must
be used, as shown in Fig. 7.
Filling of the system must be carried out in a manner approved by the local Water Undertaking. Where allowed, the system
may be filled via a temporary connection as shown in Fig. 6. After filling, always disconnect the flexible hose of the filling loop.
All fittings used in the system must be able to withstand pressures up to 3 bar.
Drain taps (to BS 2879) must be used to allow the system to be completely drained.
Note: A drain tap should be installed at the lowest
point of the heating circuit and beneath the appliance.
System
drain tap
Note: If the mains is fitted with water
meter, check valves or loose jumper stop
cock, then a DHW expansion device must
be fitted.
Static head of system
Make up vessel
DHW outlet
Mains water inlet
Additional expansion
vessel (if required)
Automatic
air vent
Boiler
casing
Heatingflow
Heatingreturn
Filling point
Double check valve assy.
Fig. 5
Fig. 6 Fig. 7
Filling loop
temporarily connected
Heating circuit
return Mains
water
supply
Stop
valve
Hose
unions
Stop
valve
Double check
valve assembly
Test cock
Feed cistern to be
located above highest
point in the system
Mains
water
supply
Stop
valve
Test cock
Double check
valve assembly
Overflow
Heating circuit
return

11
Alpha CD25C/28C/35C - General Boiler Information
3.9 FLUSHING THE HEATING SYSTEM
It is essential that the central heating system is thoroughly cleaned and flushed when fitting an Alpha CD boiler. Failure to do so
will invalidate the warranty.
The primary condensing heat exchanger is constructed in stainless steel and therefore is compatible with most materials used
in a heating system.
If a cleaning agent and inhibitor are used, they must be applied in accordance with their manufacturers instructions. Only
products from Fernox and Sentinel are acceptable for use with the Alpha CD boilers. Further information can be obtained from
Fernox (Tel: [phone]) or Sentinel (Tel: [phone]).
Although the Cyclone is fitted in the heating return on the boiler, the heating system should still be thoroughly flushed as
detailed below. The Cyclone collection point should be emptied via the drain point (see Fig. 11) after flushing has been
completed.
The system should be flushed in accordance with BS 7593 and BS 5449. The following procedures are recommended:
1. Installing onto a new system:-
a.Fill the system, vent at high points, at pump and radiators.
b.Check for leaks.
c.Rapidly drain the system.
d.If required, chemically clean the system as instructed by the recommended cleaner manufacturer.
Note: Ensure that the system is flushed to remove any remains of the cleaner.
e.If chemical cleaner is not used to clean the system:-
i) Refill the system.
ii) Switch on the boiler and allow the system to heat up to the normal operating temperature.
iii) Rapidly drain the system while the water is still hot.
iv) Refill the system.
f. As required, add the recommended inhibitor to the system as instructed by the inhibitor manufacturer.
g.Recheck for leaks.
2. Installing onto an existing system, clean the system before fitting the new boiler:-
a.If the old boiler is still working:-
i) Switch on the boiler and allow the system to heat up to the normal operating temperature.
ii) Rapidly drain the system while the water is still hot.
iii) Refill and chemically clean the system as instructed by the recommended cleaner manufacturer.
iv) Ensure the system is flushed to remove any remains of the cleaner.
v) Fit the new boiler.
b.If the old boiler is not working:-
i) Rapidly drain the system.
ii) Remove the old boiler.
iii) Flush the system through.
iv) Fit the new boiler.
v) Refill and chemically clean the system as instructed by the recommended cleaner manufacturer.
vi) Ensure the system is flushed to remove any remains of the cleaner.
c.As required, add the recommended inhibitor to the system as instructed by the inhibitor manufacturer.
d.Check for leaks.
3.10 DISPOSAL OF CONDENSATE
Provision must be made for the safe disposal of condensate produced by the flue gases of the Alpha CD boilers and reference
should be made to BS 6798: 2000 for the requirements on the disposal of condensate.
The boilers incorporate a condensate trap which has a seal of 75 mm, therefore no additional trap is required.
The condensate should ideally be discharged internally into an internal waste pipe (washing machine/sink waste) or soil pipe to
avoid the possible risk of freezing. The pipework must be in 22 mm pipe.
External pipe runs should be avoided, but if it is necessary, the pipework should be at least 32 mm and protected from the risk
of freezing with a waterproof insulation and the length should be kept to a maximum of 3 m. Termination should be into an
external gulley or soakaway as shown in Figs. 8 and 9.
Note: All pipework must have a continuous fall (see Figs. 8 and 9) from the boiler and must be of an acid resistant material
such as plastic waste pipe. (copper or steel is not suitable).
It should be noted that the connection of a condensate pipe to a drain may be subject to local building control requirements.

12 Alpha CD25C/28C/35C - General Boiler Information
Fig. 9 - External soakaway
3.11 DOMESTIC HOT WATER SYSTEM
The minimum flow rate needed for the flow switch and burner to operate is 2.5 litres/min.
The incoming mains water pressure should be between 0.2 and 8 bar to ensure efficient operation. If the pressure is above 7 bar
a pressure reducing valve must be fitted.
To ensure economic use, the pipe runs between the boiler and taps should be in 15 mm copper pipe and be as short as
possible. Where possible the pipework should be insulated to reduce heat loss.
All taps and mixing valves used with the hot water system must be suitable for operating at a mains pressure of up to 8 bar.
Showers - A shower may be used with the boiler if required.
If a loose or flexible head type shower is used it may require the fitting of a double check valve, to comply with Water Bye Law 17.
Bidets - No anti-syphonage arrangements are necessary, provided the outlets are shrouded and it is not possible to attach a
temporary hand held spray. A supply of direct mains fed hot and cold water is permitted provided the appliance is of the over-
rim flushing type.
Before the mains water supply pipe is connected to the boiler, it should be thoroughly flushed out to avoid the danger of dirt or
foreign matter entering the boiler.
Fig. 8 - External gully

13
Alpha CD25C/28C/35C - Installation
4 INSTALLATION
4.1 UNPACKING
1. The boxes required when the boiler is installed with a horizontal flue are as follows:-
Box 1 .............................Casedboilerfittedwithwaterandgasvalves,fillingloop,seasonalityvalve,unionbendsandwashers
Mounting bracket plus screws and wall plugs
Condensate discharge pipe
Literature pack and Wall template
Box 2 .............................CDEasy-Flue500mmorCDEasy-Flue1000mm.Bothinclude90°bendandhorizontalflueterminal
Note: NOT required for vertical flue
Notes: a. All flues must be suitable for CD condensing boilers.
b. CD 750 mm and 1000 mm flue extensions are available, if required.
Box 3 (if applicable) .......Premier Pack includes: wall mounting jig with template, cyclone, bottom tray,earth bonding plate,
spacers, pressure relief pipe terminal, split flow and return union bends, screw pack and fitting
instructions.
2. Unpack boiler and remove the loose items packs and mounting bracket.
Note: The boiler can be stood in an upright position, (to allow this, the union bends have been turned upwards so that they
do not protrude beneath the bottom - check this before standing the boiler upright).
4.2 CLEARANCES REQUIRED - Fig. 10
Fig. 10
4.3 PREPARE THE WALL - Figs. 11
If the optional wall jig is used refer to the
instructions supplied with the kit.
1. Decide uponthe positionof theboiler taking
into account the clearances required for
servicing and the flue terminal position.
2. Tape the template to the wall (ensure it is
level and the right way up) and mark the
position of the holes for the boiler
mounting bracket or, if applicable the wall
jig fixings. If rear exit flue is used, mark the
position of the hole for the flue.
The wall jig is supplied with a pressure
relief valve discharge pipe for use when
the boiler is mounted on an external wall
where the outside is inaccessible, if you
wish to use this pipe - mark it's position.
3. Side exit flue - Continue the horizontal
centre line of the flue across the wall to the
side wall, then along the side wall 140 mm,
180 mm if the wall jig is used (ensure the
linesarehorizontal).Thiswillgivetheposition
of the centre of the hole for the flue. Fig. 11
720 mm
300 mm
Minimum
clearance
of 450 mm
from front
of boiler
440 mm
235 mm
250 mm
5mm 5mm
Boiler
Minimum
clearances
(340 mm if
wall jig
fitted)
Template
Outline of
boiler
Wall
mounting
bracket
fixing holes
Wall jig
fixing holes
140 mm
(180 mm if wall jig used)
Ensure line is level
Rear exit hole
110mmdia.
Position of
110mmhole
to be cut for
side exit flue
130 mm
==

14
4. Cut the 110 mm diameter hole (or use a 107 mm core drill) in the wall for the flue.
Notes: 1. Ensure the hole is horizontal.
2. For internal fitting of the flue, using the flue sealing collar supplied, cut a 130 mm dia. flue hole using a 127 mm
core drill.
5. Drill the fixing holes (10 mm dia.) to accept the No.10 plugs supplied. Using the screws supplied, fit the mounting bracket or
wall jig if used. If applicable drill a 22 mm dia. hole for the pressure relief valve discharge pipe terminal supplied with the jig.
IMPORTANT: If the wall jig is used, follow the instructions supplied with the Premier Pack to fit the jig,
mount the boiler and connect the pipework.
4.4 FIT THE BOILER - Refer to Fig. 11, 12
1. Lift the boiler and locate it on the mounting bracket.
4.5 CONNECT THE PIPEWORK - Fig. 13
1. Thoroughly flush out all the water pipework. Refer to Section 3.9.
2. The valves/fittings have been factory fitted, however, check that all the
connections underneath the boiler have been tightened, especially the
union bends.
Note: If applicable the heating union bends supplied with the wall jig have
been designed to enable the heating pipes to be routed from above and/
or below using the same fitting.
Note: When soldering to the boiler union bends, ensure the bends are
not connected to the valves, otherwise the internal seals may be
damaged.
3. Connect the system pipework to the boiler.
Note: Do not forget that the pressure relief valve discharge pipe must be
routed clear of the boiler to a drain in such a manner that it may be seen,
but cannot cause injury to persons or property.
4. Connect the 22 mm condensate trap drain pipe to the condensate
discharge pipe using the clip supplied.
Ensure that the condensate discharge pipe is as required in Section 3.10.
Pour at least 0.5 litre of water into the flue duct, as shown in Fig. 12, and check the condensate discharge pipe for soundness.
5. Ensure that all the valves are closed (spindle flats at right angles to valve) and do not turn on the water or gas supplies at this stage.
Alpha CD25C/28C/35C - Installation
Fig. 12 - rear of boiler
Location for
wall mounting
bracket on
rear of boiler
Pour water into flue duct
Fig. 13a - Without wall jig
A- Heating flow (22 mm)
B- Hot water outlet (15 mm)
C- Gas inlet (22 mm)
D- Cold water mains inlet (15 mm)
E- Heating return (22 mm)
F- Pressure relief valve (15 mm)
G- Heating drain point
H- Cold water inlet filter
I- Condensate discharge pipe
Note: Disconnect the filling loop after
filling the central heating system. Heating return
valve
Filling loop
G
H
Condensate
trap
20 23
65 70 95 95 70 45
CB DFEA
Heating flow
valve
I
37 58
Seasonality
valve

15
2. Determine the overall length (L) of flue required, (see Fig. 16) as follows:-
Rear flue L = wall thickness (B) + 60 mm
Side flue L = wall thickness (B) + distance between boiler and wall (C) + 120 mm
Fig. 16
3. Adjust the telescopic section of the flue to the distance 'L', ensuring that the two labels marked 'TOP' are aligned, then seal
and secure the joint between the ducts with the sealing tape supplied.
4. Pass the flue assembly through the wall (from inside or outside).
Note: Internal fitting - If there is no access to make good the outside wall, locate the flue sealing collar onto the outer duct
of the flue immediately before the terminal grille onto the location provided. Push the flue assembly through the 130 mm flue
hole, so that the collar completely passes through the wall. Then pull the flue assembly back into the correct position. Visually
check that the collar is sealing the outside wall and that it is not restricting any of the openings of the flue terminal.
4.6 FIT THE FLUE - Figs. 14, 15
The following procedure applies to fitting an Alpha CD Easy-Flue to both rear or side exit flue - horizontally only.
1. The CD Easy-Flues are suitable for use in the flue length ranges shown in the tables below.
Note: Where the length is less than the minimum or more than the maximum, refer to Section 4.7.
Alpha CD25C/28C/35C - Installation
Fig. 14 Fig. 15
CD Easy-Flue
500 mm
1000 mm
B (mm)
Max
550
945
Min
310
705
CD Easy-Flue
500 mm
1000 mm
Max
465
860
Min
225
620
B + C (mm)
Note: Add 40 mm to
dimension B if the wall jig is
used.
Heating return
valves
Heating flow
valve
Fig. 13b - With wall jig
A- Heating flow (22 mm)
B- Hot water outlet (15 mm)
C- Gas inlet (22 mm)
D- Cold water mains inlet (15 mm)
E- Heating return (22 mm)
F- Pressure relief valve (15 mm)
G- Heating drain point
H- Cold water inlet filter
I- Cyclone
K- Wall jig
Note: Disconnect the filling loop after
filling the central heating system. Filling loop
G
H
Condensate
trap
20 23
65 70 95 95 70 45
CB D
FEA
I
37 58
K
Condensate
discharge
pipe

16
5. Position the seal and clamp (two screws) supplied, over the bend. Fit the bend to the boiler and rotate to the correct position.
Secure in position using the seal and clamp, ensuring the seal is located centrally over both the bend and boiler adaptor.
6. Fit the inside flue sealing collar over the Easy-Flue. Fit the outside flue sealing collar onto the flue immediately before the
terminal grille onto the location provided.
7. Slide the clamp (three screws) over the outer duct and pull the flue assembly towards the bend, locating the inner duct into
the seal joint on the bend. Ensure the labels marked 'TOP' are positioned at the top before securing the flue assembly to
the bend with the clamp (three screws) located centrally over the joint.
Note: Check the flue terminal protrudes 100 mm out of the wall and the inner duct of the terminal is positioned correctly
(see Fig. 18).
8. Make good the inside wall by pushing the inside flue sealing collar upto the wall.
Alpha CD25C/28C/35C - Installation
Fig. 18 - Rear flue
Flue Length
Up to maximum:-
Between:-
Between:-
Between:-
Less than:-
Rear Flue (B)
11.86 m
705 mm and 945 mm
550 mm and 705 mm
310 mm and 550 mm
310 mm
Side Flue (B + C)
11.775 m
620 mm and 860 mm
465 mm and 620 mm
225 mm and 465 mm
225 mm
Comments
Alpha CD 750 mm or 1000 mm flue extension
(Part No. 6.2000750 or 6.2001050) is required to
extend the range of telescopic flue.
Refer to Section 4.7 paragraph 2 for instructions
on how to extend the flue.
Note: A 130 mm flue hole (127 mm core drill) is
required in the wall.
Within the standard Easy-Flue 1000 mm
(Part No. 6.20001000) telescopic range.
Use an Easy-Flue 1000 mm (Part No. 6.20001000)
and the terminal may protrude somewhat from the
outside wall.
Within standard Easy-Flue 500 mm
(Part No. 6.2000500) telescopic range.
Terminal may protrude somewhat from the outside
wall.
Note: Subtract 40 mm to dimension B if the wall jig is used.
40 (80 if wall jig used)
140
(180 if wall jig used)
90
Outer duct clamp
Inner duct seal joint
Inner duct seal joint
90° bend
Terminal
Flue sealing collar
Note: Ensure the outer flue duct is horizontal
Boiler side
CD Easy-Flue
Ensure the inner duct within
the terminal is at the top.
The inner duct must
be positioned to slope towards
the boiler
Note:
4.7 EXTENDING THE FLUE - Fig. 19
Note: The maximum horizontal flue assembly length must not exceed a length of 12 metres.
1. When the flue length required is more than the maximum or less than the minimum stated in Section 4.6, paragraph 1,
refer to the table below.
Fig. 17 - Fitting the flue from inside

17
Alpha CD25C/28C/35C - Installation
2. Use the template (supplied with the boiler) to mark the required flue position and cut a 130 mm diameter hole for the flue
(use a 127 mm core drill). The size of the hole provides sufficient clearance for the clamps on the flue extension to pass
through the hole.
3. Determinethe overallflue lengthasdescribed inSection4.6,paragraph2 todeterminethenumberof AlphaCD750/1000mm
flue extensions required.
4. Assemble the flue extensions together by locating the inner duct into the seal joint and secure each extension together
with the clamps supplied (three screws). Ensure that the clamps are positioned centrally over the joints.
Note: If it is required to cut an extension, DO NOT cut the end of the inner duct that incorporates the seal joint. Ensure the
inner duct end without the seal joint is cut so that it is 15 mm longer than the outer duct.
5. Adjust the telescopic section of the Easy-Flue to the required length and secure the Easy-Flue with the sealing tape
supplied. Fit the Easy-Flue to the extensions by locating the inner duct into the seal joint and secure with the clamp (three
screws), ensuring it is located centrally over the joint.
6. Mark the end of the flue assembly 'TOP' where it is connected to the boiler,so that the 'TOP' of the flue terminal is aligned
with the 'TOP' at the boiler end of the flue assembly.
7. Pass the complete flue assembly through the wall.
8. Position the seal and clamp (two screws) supplied, over the bend. Fit the bend to the boiler and rotate to the correct
position and secure in position using the seal and clamp, ensuring that the seal is positioned centrally over both the bend
and adaptor.
9. Slide the clamp (three screws) over the outer duct and pull the flue assembly towards the bend, locating the inner duct into
the seal joint on the bend.
10. Secure the flue assembly to the bend with the clamp (three screws) ensuring it is positioned centrally over the joint,
ensuring the 'TOP' marked on the outer duct is positioned at the top.
Note: Check the flue terminal protrudes 100 mm out of the wall and that the inner duct of the terminal is positioned
correctly, i.e. the inner duct within the terminal is at the top. See Fig. 19.
11. Make good the outside wall by fitting a flue sealing collar onto the location provided immediately behind the flue terminal
grille. Make good the inside wall as required.
Note: If flue sealing collars are being used to make good the inside wall, then they will need to be fitted before assembling
the flue.
Fig. 19 - Side flue
90
25
220 220
125
Note: Ensure the flue extension slopes
downwards towards the boiler by a minimum
of 25 - 30 mm per metre Boiler front
Outer duct clamp
Inner seal joint
Inner seal joint
Flue length (L)
Clamp
and seal
90° bend
Seal joint
CD Easy-Flue
CD Flue extension
Flue sealing
collar
Flue
terminal
Ensure the inner duct within
the terminal is at the top.
The inner duct must
be positioned to slope towards
the boiler
Note:

18
Fig. 21
Alpha CD25C/28C/35C - Installation
4.8 CONNECT THE MAINS SUPPLY - Fig. 20
1. Gain access to the boiler terminal block by releasing the two fixing
screws (one each side) securing the control panel and lowering the
panel. Refer to Technical Data, Section 2.9 for connection details.
2. Note: This boiler has been fitted with a mains supply cable. However,
if it is necessary to fit an alternative supply cable, ensure the cable
clamp that has been fitted is removed and connect as follows:-
Remove the two screws securing the terminal block cover from the
back of the control box (see Fig. 20). Pass the mains supply cable
through the cable clamp and connect as follows:- Brown to L, Blue to
N and Green/Yellow to . Ensure correct polarity.
Note: Ensure that the length of the earth wire is such that if the
supply cable is pulled out of its clamp the live and neutral wires
become taut before the earth wire.
The main terminal block can be removed by pulling it off the pins to
give easy access to the terminals.
Do not switch on the electrical supply at this stage.
3. If an external control, i.e. room thermostat or external clock is to be
fitted, remove the terminal block cover and remove the link between
terminals 1 and 2. Pass the cable through the cable clamp and
connect it to terminals 1 and 2. Replace the terminal block cover.
(Refer to Section 2.9).
4. Replace the terminal block, ensuring it is located correctly on the plastic pins and replace the cover.
5. Ensurethatthereissufficientfreecabletoallowthecontrolpaneltoberaisedandloweredthentightenthecableclampscrews.
6. Leave the control panel open until commissioning procedures have been completed.
7. Carry out electrical system checks - Short circuit, Polarity, Earth continuity and Resistance to earth with a suitable multimeter.
4.9 FIT THE CLOCK KIT - Fig. 21
Ensure the electrical supply to the boiler is isolated.
Important: Only use an Alpha single channel clock. Do not fit a two channel clock.
1. Remove the two screws securing the clock cover at the rear of the control panel.
2. Remove and discard the clock blanking panel.
3. Insert the clock into the opening and secure in place with the screws supplied.
4. Disconnect the clock wiring from the terminal block and connect it to the clock as follows:-
Blue wire to terminal 1, Brown wire to terminal 2 and Red wires to terminals 3 and 4, (or as per the instructions supplied with
the clock). Ensure wiring is correct.
5. Replace the clock cover. Do not overtighten the fixing screws.
6. Leave the control panel open until commissioning procedures have been completed.
Rear of
control
panel
Cover
Grommets
Cable
clamps
Fuse
Remove link
to connect
external
controls
Fig. 20
Rear of control panel
Clock cover
Grommets
Clock fixing pillars

19
Alpha CD25C/28C/35C - Commissioning
5 COMMISSIONING
When commissioning the boiler, ensure the Benchmark Checklist is completed.
5.1 FILL THE SYSTEM
1. The boiler is fitted with an automatic air vent positioned on the pump (see Fig. 2), ensure that the vent is always open.
2. Open the central heating flow and return valves (slot in-line with valve) (see Fig. 13).
3. Open the fill point valve on the filling loop until water is heard to flow. To aid venting, the boiler drain point (see Fig. 2) may
be opened until water flows out. Close the drain point as soon as water appears.
4. To remove the air - Vent each radiator in turn, starting with the lowest in the system.
5. Itisimportantthat thepump isproperly ventedto avoiditrunningdryanddamagingits bearings.Unscrew andremove thecap
from the centre of the pump. Using a suitable screwdriver rotate the exposed spindle about half a turn, then replace the cap.
6. Check the operation of the pressure relief valve (see Fig. 2) by turning the head anti-clockwise until it clicks. The click is
the valve lifting off its seat allowing water to escape from the system - check that this is actually happening.
7. Continue to fill the system until the pressure gauge indicates 1.0 bar. Close the fill point valve and check the system for
water soundness, rectifying where necessary. Disconnect the filling loop from the mains supply.
Water may be released from the system by manually operating the drain point (see Fig. 2) until the system design
pressure is obtained. The system design pressure (cold) should be between 0.75 and 1.25 bar.
Refer to Sections 3.7 and 3.8. System volume, Flushing and Filling the system.
8. Open the mains water inlet valve (see Fig. 13). Turn on all hot water taps and allow water to flow until no air is present.
Turn off taps.
9. Ensure that the condensate trap has been filled with water. Refer to Section 4.5, paragraph 4.
5.2 BOILER CONTROLS - Fig. 22
Fig. 22
01
2
3
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
bar
04
3
2
1
RESET
A
D
B
C
SELECTOR THERMOSTAT THERMOSTAT
OFF
Clock (if fitted)
Indicator
Neons
Selector Switch
Domestic
Hot Water Thermostat
Central
Heating Thermostat
System
Pressure Gauge
5.3 TEST FOR GAS SOUNDNESS AND PURGE THE SUPPLY
1. With the boiler gas service cock closed (slot at right angles to valve). Pressure test the gas supply and inlet pipework
connection to the boiler gas service cock for soundness in accordance with BS 6891.
2. Loosen the gas inlet pressure test point screw on the gas valve (see Fig. 23). Ensure the gas supply is on and open the
boiler service cock to purge in accordance with BS 6891.
3. Retighten the test point screw and test for gas soundness. Close the boiler gas service cock.

20
5.4 INITIAL LIGHTING - Refer to Fig. 22
1. Ensure that the gas and electrical supplies to the boiler are off and that the mains water inlet valve and the central heating
flow and return valves are open.
2. Turn on the gas and electrical supplies to the boiler.
3. Ensure all external controls are calling for heat.
If the optional Clock is fitted, refer to the User's instructions, set the time and ensure the Clock is in an 'on' mode.
4. Set the hot water and central heating thermostats to maximum.
5. Set the selector switch to (DHW only). Open a hot water tap, the main burner will light and the boiler will provide hot
water. Close the tap and the burner will go out.
6. Set the selector switch to (CH and DHW). The boiler will now run in the central heating mode. The pump will start,
the fan will start and the main gas valve solenoid will open allowing the main burner to light.
5.5 CHECK THE BURNER PRESSURES - Figs. 23, 24
Turn the boiler off. Remove the two pressure test point screws at the top of the boiler and
connect a differential pressure gauge to P1 and P2 as shown in Fig 24. Allow the boiler to
run for 10 minutes and check the differential burner pressures.
Hot water mode
1. Set the selector switch to (DHW only) and fully open a hot water tap.
2. The burner will light at the ignition rate and the burner pressure will increase to
maximum.
3. Graduallyclosethehottapandcheckthattheburnerpressuredecreasestoitsminimum.
Fullyopenthetapandcheckthattheburnerpressureincreases.Closethetapandcheck
that the burner goes off.
Note: The burner pressure settings have been factory set and do not require
adjusting. If incorrect, check that the inlet gas pressure is 20 mbar.
If the inlet gas pressure is not 20 mbar, either the pipework is too
small or the gas supply to the house is insufficient, in which case
contact your gas supplier.
Central heating mode
1. Set the selector switch to (DHW and CH).
2. The burner will light at the ignition rate and will increase to the
factory pre-set maximum output after 1 minute.
3. Turn off the boiler. Disconnect the pressure gauge and tighten
the test point screws.
Test for gas soundness using suitable leak detection fluid.
Note: Refer to Technical Data, Section 2.1 for the required
differential burner pressures.
5.6 FINAL COMMISSIONING
1. Allow the heating system to heat up, then balance the system to achieve the necessary temperature difference across the
heating flow and return pipes at the boiler and check the system volume and pressure. (Refer to Technical Data, Sections
2.2 and 2.8).
2. Turn off the boiler.
3. Thoroughlyflushoutthewaterpipework(refertoSection3.9)andwithnopressureintheboilerheatingcircuit,emptythecyclone
(if applicable) at it's drain point (see Fig. 13) of any debris. Clean the mains water inlet filter (see Fig. 13).
4. Re-pressurise the system as described in Section 5.1.
Alpha CD25C/28C/35C - Commissioning
Fig. 23
Do not
connect
here
Do not connect here
Inlet gas
pressure
test point
Fig. 24
++
-
-
P1P2
Flue sample
point (marked 'F')
-+