Alpha Alpha CB24 User guide

Installation and Servicing
Instructions
Alpha CB24/28
Range of Wall Mounted, Fan Assisted, Room Sealed,
Gas Fired Combination Boilers
Nepicar House, London Road,
Wrotham Heath, Sevenoaks,
Kent TN15 7RS
For Technical help or for Service call ...
ALPHA HELPLINE
Tel: [phone]
Alpha CB24X G.C. No. 47 532 14
Alpha CB24 G.C. No. 47 532 15
Alpha CB28 G.C. No. 47 532 16
Alpha CB28X G.C. No. 47 532 17
Service Listed
For use with Natural Gas only
Leave these instructions with the User

2Alpha CB24/28 - Contents/Introduction
CONTENTS
1 Introduction ....................................... 2
2 Technical data................................... 3
3 Generalboilerinformation.................. 6
4 Installation......................................... 10
5 Commissioning ................................. 15
6 Boileroperation ................................. 17
7 Routine servicing............................... 18
8 Componentreplacement ................... 20
9 Wiringdiagrams ................................ 27
10 Faultfinding ...................................... 29
11 Short parts list ................................... 33
12 Service history .................................. 34
The Alpha CB range of boilers are wall mounted, fan assisted room-sealed combination boilers. The burner is lit electronically
and the heat output is controlled by a modulating gas valve.
The boilers, providing both central heating and domestic hot water at mains pressure, are designed for use with a fully
pumped, sealed and pressurised heating system using only Natural Gas.
The boilers are supplied with a pump, diverter valve, pressure relief valve, expansion vessel and pressure gauge fully
assembled and tested.
As supplied, the Alpha CB24 boilers will automatically modulate to provide central heating outputs between 9.3 and 23.3 kW
(31 700 and 79 500 Btu/h). The Alpha CB28 boilers will provide central heating outputs between 11.2 and 28.0 kW (38 200
and 95 500 Btu/h).
The maximum output available for domestic hot water is 23.3 kW (79 500 Btu/h), capable of providing 9.5 litres/min with a
temperature rise of 35°C for the Alpha CB24 boilers, and 28.0 kW (95 500 Btu/h), capable of providing 11.4 litres/min with a
temperature rise of 35°C for the Alpha CB28 boilers.
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
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.
Note: Ensure that the Benchmark Log Book has been completed after the boiler has been installed and commissioned.
1 INTRODUCTION

3
2.1 PERFORMANCE - NATURAL GAS
2 TECHNICAL DATA
Alpha CB24/28 - Technical Data
Min. Clearances for Servicing Top
(from casing) Bottom
Sides
Front
Flue Terminal Size
Flue Terminal Protruding
Hole Size Required For Flue Assy.
Lift Weight 24/24X
28/28X
2.4 INSTALLATION
220 mm
250 mm
5 mm
450 mm
100 mm Dia.
145 mm
110 mm Dia.
41 kg
42 kg
MAX.
28.4
96 900
23.3
79 500
10.7
4.28
2.71
95.70
MIN.
12.1
41 300
9.3
31 700
2.2
0.9
1.16
40.96
Room sealed chamber
panel fitted
Central Heating
Heat Input kW
(Gross) Btu/h
Heat Output (modulating) kW
Btu/h
Burner Pressure mbar
Settings in wg
Gas Rate m³/h
ft³/h
MAX.
34.0
116 000
28.0
95 500
11.7
4.68
3.25
114.8
MIN.
14.3
48 800
11.2
38 200
2.5
1.0
1.37
48.38
Room sealed chamber
panel fitted
Central Heating
Heat Input kW
(Gross) Btu/h
Heat Output (modulating) kW
Btu/h
Burner Pressure mbar
Settings in wg
Gas Rate m³/h
ft³/h
MAX.
28.4
96 900
23.3
79 500
10.7
4.28
2.71
95.70
9.5
2.1
MIN.
12.1
41 300
9.3
31 700
2.2
0.9
1.16
40.96
Domestic Hot Water
Heat Input kW
(Gross) Btu/h
Output to Water (modulating) kW
Btu/h
Burner Pressure mbar
Settings in wg
Gas Rate m³/h
ft³/h
Flow Rate at 35°C Rise L/min
G.P.M.
Room sealed chamber
panel fitted
MAX.
34.0
116 000
28.0
95 500
11.7
4.68
3.25
114.8
11.4
2.5
MIN.
14.3
48 800
11.2
38 200
2.5
1.0
1.37
48.38
Domestic Hot Water
Heat Input kW
(Gross) Btu/h
Output to Water (modulating) kW
Btu/h
Burner Pressure mbar
Settings in wg
Gas Rate m³/h
ft³/h
Flow Rate at 35°C Rise L/min
G.P.M.
Room sealed chamber
panel fitted
Burner
Main Heat exchanger
DHW Heat Exchanger
Main Burner Injectors 24/24X
28/28X
Flue - Outer Duct
Flue - Inner Duct
Stainless steel
Copper
Stainless Steel
1.30 mm (x12)
1.30 mm (x14)
White
Aluminium
2.3 COMPONENTS
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 24/24X
28/28X
Outlet Water Temp. (Approx. max.)
8 bar
0.2 bar
2.5 l/min
15 mm
15 mm
0.2 L
0.24 L
62°C (144°F)
2.2 SYSTEM
Alpha CB24 and CB24X Alpha CB28 and CB28X
Alpha CB24 and CB24X Alpha CB28 and CB28X

4Alpha CB24/28 - Technical Data
Fig. 1
720 mm
450 mm
330 mm
22 mm
1.6 L
1.8 L
100 mm
60 mm
Case Dimensions Height
(without bottom tray) Width
Depth
Gas Connection
Primary Water Content 24/24X
28/28X
Air Duct Diameter
Flue Duct Diameter
2.5 GENERAL 2.6 ELECTRICAL
Supply
External Fuse
Power Consumption
Internal Fuse
Electrode Spark Gap
230/240 V ~ 50 Hz
3 A
170 W
F2 A
2 to 4 mm
2.7 FLUE LENGTHS
Flue length = 0.75 m (not including the terminal, which is supplied with the boiler)
Note: Additional flues (of the same length) are available.
Length of Flue Required:-
Rear Flue = wall thickness + 175mm
Side Flue = wall thickness + distance between wall and side of boiler + 185 mm
Vertical Flue = distance from top of boiler side panel to required roof position minus 1 m for vertical terminal assembly
Maximum flue length = 4 m
Each additional 90° Bend is equivalent to 1 m of flue length
Each 45° Bend is equivalent to 0.5 m of flue length
The Vertical Flue terminal assembly is equivalent to 1 m of flue length
2.8 AVAILABLE PUMP HEAD FOR CENTRAL HEATING
gal/min
3.7
2.8
2.3
1.8
1.5
Btu/h
79 500
60 000
50 000
40 000
31 700
kW
23.3
17.58
14.65
11.63
9.3
metres
2.4
3.8
4.5
5.1
5.45
feet
7.9
12.5
14.8
16.7
17.9
Output Available pump head
metres
3.2
4.4
4.8
5.35
5.65
feet
10.5
14.4
15.8
17.5
18.5
metres
2.5
1.9
1.25
0.8
0.5
feet
8.2
6.2
4.1
2.6
1.6
metres
2.3
1.3
0.95
0.65
0.4
feet
7.5
4.3
3.1
2.1
1.3
Pressure loss across boiler
gal/min
4.3
3.3
2.7
2.2
1.7
litre/min
16.7
12.6
10.5
8.3
6.7
17°C 20°C litre/min
19.6
14.8
12.3
9.8
7.8
17°C 20°C 17°C 20°C
Flow rate
This information is based on 17°C and 20°C system design temperature difference.
Note: For outputs upto 28 kW refer to section 3.7.
Boiler terminal block
1. Ensure wires are connected
correctly
2. Only fit the Alpha recommended
clock. Other clocks could cause
damage.
WARNING
Blue
Wire
Brown
Wire
Red
Wire
12345Internal Clock Terminals
Red
Wire
Not
Used
Clock connections
2.9 ELECTRICAL CONNECTIONS
Note: This Appliance Must Be Earthed
An optional integral Clock kit is available if required.

5
2.10 BOILER SCHEMATIC
Alpha CB24/28 - Technical Data
1 - Seasonality valve (N/A to 24X/28X)
1 - Flow regulator (24X/28X)
2 - DHW switch
3 - Diverter valve and DHW flow valve
4 - Gas valve
5 - Primary temperature sensor
6 - DHW heat exchanger
7 - Main burner
8 - Primary heat exchanger
9 - Room sealed chamber
10 - Fan
11 - Air pressure switch
12 - Flue hood
13 - Overheat thermostat
14 - Expansion vessel Fig. 2
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 (N/A to 24X/28X)
23 - Flue sampling point
24 - Gas service cock
25 - Mains inlet on/off valve
26 - On/off valve (2 off)
27 - Automatic by-pass (N/A to 24X/28X)
28 - Cyclone separator (N/A to 24X/28X)

6
3.1 GAS SUPPLY
The Alpha CB24 and CB24X boilers require a gas rate of 2.71 m³/h (95.7 ft³/h) and the Alpha CB28 and CB28X a gas rate
of 3.25 m³/h (114.8 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 there is a slight downward slope towards the terminal.
Flue components are available as follows:-
Top easy-flue 500 mm (includes 90° bend), refer to separate instructions
0.75 m flue
90° bend
45° bend
Vertical flue terminal assembly. Refer to the separate installation instructions supplied with the assembly.
A Twin Pipe Flue system is available for use with all the boilers in the range. Refer to the separate instructions for details.
The following methods determine the correct length of flue required.
For rear exit flue L = B + 175 mm
For side exit flue L = B + C + 185 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 m. Each 45° bend used reduces the maximum
flue length by 500 mm.
2. Under no circumstances must the flue length (including allowances for extra bends) exceed 4 metres.
3. FailuretouseAlphafluecomponentswiththeboilerwillinvalidatetheboilersCEapproval,guaranteeandmaybeunsafe.
3 GENERAL BOILER INFORMATION
Alpha CB24/28 - General Boiler Information

7
HORIZONTAL FLUE OPTIONS - Lmax = 4 metres
L = B + C + E + 185 mm
Alpha CB24/28 - General Boiler Information
L = B + C + 185 mm
CB
E
CB
E
B
F
B
C
L = B + E + F + 185 mm + (90° bend = 1 metre)
L = B + C + 185 mm + (2 x 45° bends = 1 metre)
Fig. 3
VERTICAL FLUE OPTIONS

8
3.5 FLUE TERMINAL LOCATION - Fig. 4
A Directly below an opening, air brick, windows, etc.
B Below gutters, soil pipes or drain pipes
C Below eaves
D Below balconies or car port roof
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 facing the terminal
I From a terminal facing the terminal
J From an opening in the car port (e.g. door, window) into dwelling
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.
300 mm
75 mm
25 mm
25 mm
25 mm
25 mm
300 mm
600 mm
1200 mm
1200 mm
1500 mm
300 mm
300 mm
Min. distance
Terminal position
Fig. 4
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.
In certain weather conditions the terminal may emit a plume of steam. Avoid positioning the terminal where this may cause a nuisance.
If the terminal is fitted within 850 mm of a plastic or painted gutter or 450 mm of painted eaves or 300 mm of a plastic car port
roof, an aluminium shield at least 1 m long should be fitted to the underside of the gutter or painted surface. If the terminal is
fitted less than 2 m above a surface to which people have access, the terminal must be protected by a terminal guard.
A suitable guard is available from:
Tower Flue Components Ltd., Vale Rise, Tonbridge, Kent TN9 1TB
3.6 BOILER LOCATION
The boiler is not suitable for external installation.
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 British Gas publication 'Guide for
Gas Installations in Timber Frame Housing', reference DM2.
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 CB24/28 - General Boiler Information

9
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). For guidance on water contents contact Alpha Therm Ltd. for Technical Data Sheet 15.
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, 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 a by-pass. However, where all radiators are fitted with thermostatic radiator valves it is
recommended that a system by-pass, preferably automatic, is fitted.
Cyclone (N/A CB24X/28X) - This is a device fitted in the heating return within the boiler to remove any foreign or solid matter
etc. from the system.
Alpha CB24/28 - General Boiler Information
Fig. 6 Fig. 7
3.8 FILLING THE CENTRAL HEATING SYSTEM - Figs. 6, 7
Thesystemdesignpressure (cold) shouldbe setto1.0bar.Thispressure isequivalent toa statichead (seeFig.5)of10.2 metres ofwater.
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.
Although the Cyclone is fitted in the heating return, the heating system should still be thoroughly flushed before the boiler is
connected and again after the first heating. The Cyclone collection point should be emptied via it's drain point (see Fig. 11) after
flushing has been completed.
If it is required to add inhibitor to the system, refer to Alpha Therm Ltd. for guidance.
Refer to BS 5449 and BS 6798 for further information.
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
Heating flow
Heatingreturn
Filling point
Double check valve assy.
Note: If required, an automatic by-pass is
preferred.
Heating
by-pass
(If required)
Fig. 5
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

10 Alpha CB24/28 - General Boiler Information/Installation
4 INSTALLATION
4.1 UNPACKING
1. The boxes required when the boiler is installed with a horizontal flue are as follows:-
Box 1 Cased boiler fitted with water and gas valves, filling loop, union bends and washers
Mounting bracket plus screws and wall plugs
Flue terminal and flue sealing collar plus 2 screws
Literature pack and Wall template
Box 2 90° flue bend (not required for vertical flue)
Box 3 0.75 m flue (for side and rear flue) with two clamps and inner duct support
Note: If an Easy flue 500 mm is ordered, this will be supplied instead of boxes 2 and 3.
2. Unpack boiler and remove the loose items packs, i.e. mounting bracket, flue terminal and collar.
Note: The boiler can be stood in an upright position supported by the bottom tray, (to allow this, the union bends have
been turned upwards so that they do not protrude beneath the bottom tray - check this before standing the boiler on the
bottom tray).
4.2 CLEARANCES REQUIRED - Fig. 8
3.9 DOMESTIC HOT WATER SYSTEM
The minimum flow rate needed for the flow switch and burner to operate is 2.0 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.
The mains water supply connection to the boiler must be the first connection from the mains supply.
Seasonality valve - When this valve has been set to give the temperature of hot water required by the user, it will automatically
maintain the set hot water temperature for both summer and winter conditions by automatically changing the flow rate through
the boiler.
Fig. 8