Installation and Servicing
Instructions
Alpha CD50
Wall Mounted, Fan Assisted, Room Sealed, Gas Fired,
High Efficiency, Condensing Combination Boiler with
Unvented Hot Water Storage
For Technical help or for Service call ...
ALPHA HELPLINE
T el: 0870 3001964
Nepicar House, London Road,
Wrotham Heath, Sev enoaks ,
K ent TN15 7RS
*HEJEID/=I
Service Listed
Alpha CD50 G.C. No. 47 532 24
For use with Natural Gas only
Leave these instructions with the User
CONTENTS
1 Introduction ....................................... 2
2 Technical data...................................3
3 General boiler information..................7
4 Installation......................................... 14
5 Commissioning ................................. 20
6 Boiler operation ................................. 23
7 Routine servicing...............................24
8 Component replacement ................... 26
9 Wiring diagrams ................................ 33
10 Fault Finding ..................................... 35
11 Short parts list ................................... 39
12 Service history .................................. 40
1 INTRODUCTION
The Alpha CD50 is a wall mounted, high efficiency, fan assisted, room-sealed, condensing combination boiler - incorporating a
52 litre unvented hot water storage cylinder. The burner is lit electronically and the heat output is controlled by a modulating
fan and gas valve.
The boiler, providing both central heating and domestic hot water at mains pressure, is designed for use with a fully pumped,
sealed and pressurised heating system using only Natural Gas.
The boiler is supplied with a pump, diverter valve, pressure relief valve, expansion vessel and pressure gauge fully assembled
and tested.
As supplied, the boiler will automatically modulate to provide central heating outputs between 6.3 and 29.7 kW (21 500 and
101 430 Btu/h).
The maximum output available for domestic hot water is 32.0 kW (109 200 Btu/h) and provides hot water at temperatures of up
to 65°C and flow rates of up to 18 litres/min (4 gal/min).
IMPORTANT
This boiler has been approved to the Building Regulations for unvented hot water storage systems and the Local Authority
must be notified of the intention to install. Therefore the installation must be carried out by a person competent to install
unvented hot water systems.
It is the law that all gas appliances are installed by a competent person, ie CORGI registered personnel, in accordance with
the following recommendations:-
Gas Safety (Installation and Use) Regulations 1984 (as amended)
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
Local Water Bye Laws
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.
Notes: 1. Ensure that the Benchmark Log Book has been completed after the boiler has been installed and commissioned.
2. Ensure that the appliance has been supplied with an Alpha CD flue system.
Alpha CD50 - Contents/Introduction
2
2 TECHNICAL DATA
2.1 PERFORMANCE - NATURAL GAS (CAT: 2H-G20-20 mbar)
Central Heating
Heat Input (H
)kW
s
(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
Room sealed
chamber panel
fitted
Gas Rate m³/h
ft³/h
MAX.
31.0
105 770
28.0
95 230
29.7
101 430
27.6
94 130
2.91
1.16
2.95
104.1
2.2 SYSTEM
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)
MIN.
7.4
25 360
6.6
22 830
7.0
23 980
6.5
21 500
0.27
0.11
0.71
25.1
Domestic Hot Water
Heat Input (H
)kW
s
(Gross) Btu/h
Heat Input (Hi)kW
(Net) Btu/h
Output to Water (Hs)kW
(modulating) Btu/h
Differential Burner mbar
Pressure in wg
Room sealed
chamber panel
fitted
Gas Rate m³/h
ft³/h
Flow Rate L/min
G.P.M.
Outlet Water Temp. (Approx.) °C
°F
MAX.
36.1
123 190
32.6
110 910
32.0
109 200
3.70
1.48
3.44
121.4
18.0
4.0
65
149
Time to raise water store by 50°C
Reheat time for 70% of store
(boiler ON)
(boiler OFF)
MIN.
25 360
22 830
21 500
0.27
0.11
0.71
25.1
0.22
7 minutes
3 minutes
5 minutes
Domestic Hot Water
Max. Hot Water Working Pressure
Max. Mains Inlet Pressure (inlet of pressure reducing valve)
Min. Mains Water Pressure
Mains Inlet Connection
DHW Outlet Connection
DHW Water Storage
Expansion Vessel Size (pre-charge press.)
Pressure Reducing Valve Setting
Temperature and Pressure Relief Valve
Expansion Relief Valve Setting
5.5 bar
12 bar
0.1 bar
15 mm
15 mm
52 L
4 L at 2.5 bar
2.5 bar
90°C/7 bar
6 bar
7.4
6.6
6.3
1.0
5
41
2.3 COMPONENTS 2.4 ELECTRICAL
Burner
Main Heat Exchanger
DHW Storage Cylinder
Main Burner Injector
Flue - Outer Duct
Flue - Inner Duct
2.5 INSTALLATION
Min. Clearances for Servicing Top
(from casing) Bottom
Flue Terminal Size
Flue Terminal Protruding
Hole Size Required For Flue Assy.
Lift Weight
Weight Full and Operational
Stainless steel
Stainless steel
Stainless Steel
Sides
Front
6.6 mm
White
Plastic
220 mm
250 mm
10 mm
450 mm
100 mm Dia.
100 mm
110 mm Dia.
70 kg
130 kg
Supply
External Fuse
Power Consumption
Internal Fuse
Electrode Spark Gap
2.6 GENERAL
Case Dimensions Height
Gas Connection
Primary Water Content
Air Duct Diameter
Flue Duct Diameter
230/240 V ~ 50 Hz
3 A
140 W
F2 A
3 - 4 mm
900 mm
Width
Depth
600 mm
450 mm
22 mm
3.2 L
100 mm
60 mm
Alpha CD50 - Technical Data
3
2.7 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 flue extensions are available.
Length of Flue Required:-
Rear Flue = wall thickness + 170 mm (includes terminal)
Side Flue = wall thickness + distance between wall and side of boiler + 230 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.
2.8 AVAILABLE PUMP HEAD FOR CENTRAL HEATING
Output (50/30°C) Available pump head
kW
25.40
18.70
15.60
12.35
5.30
Btu/h
86 700
64 000
53 000
42 200
18 100
20°C 20°C
metres
2.3
3.5
3.8
4.0
4.6
feet
7.6
11.6
12.6
13.2
15.2
Flow rate
litre/min
16.6
12.6
10.5
8.3
3.2
gal/min
3.7
2.8
2.3
1.8
0.7
This information is based on 20°C system design temperature difference.
Note: For outputs upto 30 kW refer to section 3.7.
2.9 ELECTRICAL CONNECTIONS
Note: This Appliance Must Be Earthed
An optional integral Clock kit is available if required.
Blue
Red
Wire
Brown
Wire
Wire
12345
Red
Not
Wire
Used
Internal Clock Terminals
WARNING
1. Ensure wires are connected
correctly
2. Only fit the Alpha recommended
clock. Other clocks could cause
damage.
Clock connections
Alpha CD50 - Technical Data
4
Boiler terminal block
Fig. 1
2.10 BOILER SCHEMATIC
1 Flue sampling point
2 Flue thermostat
3 Injector
4 Gas valve
5 Primary temperature sensor
6 Venturi
7 Main burner
8 Primary/condensing heat exchanger
9 Room sealed chamber
10 Fan
11 Pressure differential test points
12 Flue hood
13 Overheat thermostat
14 CH Expansion vessel
15 Automatic air vent
16 Pump
17 Drain point
18 Pressure gauge
19 Primary pressure switch
20 Ignition electrodes
21 Flame sensing electrode
22 Venturi negative point
23 Venturi positive point
24 Gas service cock
25 On/off valve (2 off)
26 Automatic by-pass
27 Cyclone separator
28 Condensate trap
Fig. 2
29 CH Pressure Relief Valve
30 DHW Expansion Vessel
31 DHW Storage Temperature Sensor
32 DHW Temperature/Pressure Relief Valve
33 Storage Cylinder
34 Secondary Heat Exchanger
35 DHW Drain Point
36 DHW Expansion Relief Valve
37 Mains Inlet Filter
38 Check Valve
39 Mains Inlet Valve
40 Pressure Reducing Valve with Filter
41 Automatic Flow Regulator
42 Tundish
43 Diverter Valve
Alpha CD50 - Technical Data
5
3 GENERAL BOILER INFORMATION
3.1 GAS SUPPLY
The Alpha CD50 boiler requires a gas rate of 3.44 m³/h (121.4 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 flue assembly is horizontal and the inner duct is sloping downwards towards the boiler.
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. 6.20001000.
CD 0.75 m flue extension - Part No. 6.2000750.
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 + 240 mm
For side exit flue (including terminal) L = B + C + X (L/H side X = 185 mm, R/H side X = 425 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 top of terminal
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.
Alpha CD50 - General Boiler Information
6
HORIZONTAL FLUE OPTIONS
Lmax = 12 metres (L/H side X = 185 mm, R/H side X = 425 mm)
L = B + C + X
C
E
L = B + E + F + X + (90° bend = 1.3 metre)
B
B
F
L = B + C + E + X
C
E
C
B
B
VERTICAL FLUE OPTIONS
L = B + C + X + (2 x 45° bends = 1.8 metre)
max = 15 metres Hmax = 13.2 metres
H
Fig. 3
Alpha CD50 - General Boiler Information
7
3.5 FLUE TERMINAL LOCATION - Fig. 4
Fig. 4
Terminal position
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.
Min. distance
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
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, H, J and M in the above table.
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.
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 you local boiler merchant.
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, i.e. 130 kg. 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 roomsealed 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 CD50 - General Boiler Information
8
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 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 a by-pass, however where all radiators are fitted with thermostatic radiator valves it is
recommended a system by-pass, preferably automatic is fitted.
Cyclone - This is a device fitted in the heating return within the boiler to remove any foreign or solid matter etc. from the system.
Fig. 5
3.8 FILLING THE CENTRAL HEATING SYSTEM - Figs. 6, 7
The system design pressure (cold) should be set to 1.0 bar. This pressure is equivalent to a static head (see Fig. 5) of 10.2 metres of water.
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.
Mains
water
supply
Feed cistern to be
located above highest
point in the system
Heating circuit
return
Stop
valve
temporarily connected
Hose
unions
Filling loop
Double check
valve assembly
Test cock
Stop
valve
Mains
water
supply
Heating circuit
return
Double check
valve assembly
Test cock
Overflow
Stop
valve
Fig. 6 Fig. 7
Alpha CD50 - General Boiler Information
9
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 and 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: 0179 9521133) or Sentinel (Tel: 0151 4209563).
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 it's drain point (see Fig. 13) 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.
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 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.
Alpha CD50 - General Boiler Information
10
Fig. 8 - External gully
Fig. 9 - External soakaway
3.11 DOMESTIC HOT WATER SYSTEM
The mains water supply must be first connected to the pressure reducing valve (supplied with the boiler) which will regulate the
water supply to 2.5 bar. However, all taps and mixing valves used with the hot water system must be suitable for operating at a
pressure of up to 5.5 bar.
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.
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 and the filter incorporated within the pressure reducing valve cleaned.
The stored water temperature is adjustable to a maximum of 65°C. In hard water areas this should avoid possible scale build-up,
although it is still advisable to reduce the DHW thermostat setting in such areas. However, if descaling is necessary contact Alpha
Therm Ltd. for guidance.
Alpha CD50 - General Boiler Information
11
3.12 UNVENTED HOT WATER STORAGE SYSTEM
The installation is subject to Building Regulations approval and the Local Authority must be notified of the intention to install.
The CB50 boiler is supplied with all the components required for an unvented hot water system, i.e. temperature/pressure and
expansion relief valves, expansion vessel, check valve and tundish. All these components are factory fitted, except for the
tundish which must be installed as follows:-
Discharge pipe - The discharge pipes from the temperature/pressure and expansion relief valves must be routed to the
tundish supplied and in 15 mm pipe. The discharge pipework from both relief valves may be joined together in the same sized
pipe, providing at least 22 mm pipework is connected downstream of the tundish.
Stop valve
Cold water supply
2.5 bar pressure
reducing valve
(supplied)
Filter
Mains
water
supply
Temperature/pressure
4L DHW expansion vessel
6 bar expansion
Check
valve
relief valve
Tundish
22 mm discharge
relief valve
pipe
Hot
water
Storage cylinder
Diverter
valve
Heating
Primary
Pump
Boiler
flow
Primary return
Fig. 10
Tundish - The tundish must be positioned within 500 mm of the appliance, so that it is visible to the User and away from electrical
devices. The minimum size of the discharge pipe downstream of the tundish is given in the following table.
Sizing of copper discharge pipe 'D2' - refer also to Fig. 11Table 1
Valve
outlet size
G½
Minimum size of discharge
pipe 'D1' to tundish
15 mm
Minimum size of discharge
pipe 'D2' from tundish
22 mm
28 mm
35 mm
Maximum resistance allowed,
expressed as a length of straight
pipe (i.e. no elbows or bends)
up to 9 m
up to 18 m
up to 27 m
Resistance created
by each elbow
or bend
0.8 m
1.0 m
1.4 m
The discharge pipework from the tundish:-
1. Shall fall continuously through its length.
2. Shall be of a heat resistant material, e.g. metal.
3. Shall not be fitted with any valves or taps.
4. Shall discharge to a safe visible position, e.g. onto the surface of an external wall or into a gulley.
5. Shall have a minimum of 300 mm straight pipework directly from the tundish.
Note: Where children may play or otherwise come into contact with discharges, a wire cage or similar guard must be
positioned to prevent contact whilst maintaining visibility.
Alpha CD50 - General Boiler Information
12
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