Alpha CB28X Service manual

Instructions for setting the burner
pressure on a replacement gas valve
Alpha HE/CB/SY/C Boiler Range
1. GENERAL
The maximum and minimum burner pressures are factory set and should not require adjustment. However, if the gas valve
has been replaced, then these burner pressures must be set by adjustment on the gas valve.
Refer to the Installation and Servicing instructions for gaining access to and for replacement of the gas valve.
Note: Ensure that the plastic tube between the gas valve and the room sealed chamber is correctly fitted.
2. SETTING THE MAXIMUM BURNER PRESSURE
a. Loosen the burner pressure test point on the gas valve (see
Fig. 1) and connect a pressure gauge.
b. Remove the end cap (A in Fig. 1) to reveal the two adjustment
nuts (B and C in Fig. 1).
c. Set the selector switch to (DHW only) and turn the hot
water thermostat to the maximum position.
d. Fully open a hot water tap to give the maximum water flow rate.
e. Using an 8 mm spanner, turn the maximum adjustment nut (C in
Fig. 1) to set the maximum burner pressure (see table below). If
the burner fails to light, continue to turn the adjustment nut (C)
clockwise until a burner pressure is obtained. During this
adjustment the selector switch may have to be turned to 'RESET'.
If so, wait 30 seconds each time before resetting.
Note: Clockwise to Increase the pressure. Anticlockwise to Decrease the pressure.
3. SETTING THE MINIMUM BURNER PRESSURE
a. After the maximum burner pressure has been achieved, the minimum pressure can be adjusted by removing one of the
modulating coil (Black) wires. The burner pressure will now be at the minimum setting.
b. Using a 5 mm spanner, turn the minimum adjustment nut (B in Fig. 1) to set the minimum burner pressure (see table below).
Note: It is advisable to hold the maximum adjustment nut (C) with an 8 mm spanner, when adjusting the minimum nut (B).
c. Reconnect the modulating coil (Black) wire and recheck the maximum pressure. Continue to readjust and recheck until
both the maximum and minimum burner pressures are as shown in the table.
d. Disconnect the pressure gauge and tighten the test point screw.
e. Test for gas soundness using a suitable leak detection fluid.
Fig. 1
Maximum Burner Pressure
Nat. Gas LPG
mbar
10.7
11.7
10.0
10.9
11.3
12.3
11.6
mbar
35.5
36.0
36.7
36.0
36.9
32.3
32.1
in w.g.
4.28
4.68
4.00
4.36
4.52
4.92
4.64
in w.g.
14.20
14.40
14.70
14.40
14.76
12.92
12.84
Boiler
CB24, CB24X, SY24
CB28, CB28X
CB50
C23
C27
HECB25, HESY25
HECB33
Minimum Burner Pressure
Nat. Gas LPG
mbar
2.2
2.5
1.7
2.3
2.15
1.9
1.2
mbar
7.2
7.5
6.5
7.3
7.0
5.6
4.7
in w.g.
0.90
1.00
0.68
0.90
0.90
0.76
0.48
in w.g.
2.90
3.00
2.60
2.92
2.80
2.24
1.88
These instructions have been carefully prepared but we reserve the right to
alter the specification at any time in the interest of product improvement.
© Alpha Therm Limited 2005.
Alpha Therm Limited.
Nepicar House, London Road, Wrotham Heath,
Sevenoaks, Kent TN15 7RS
Tel: [phone]
email: [email protected]
website: www.alpha-boilers.com
Compiled and designed by Publications 2000, Tel [phone]/D134