Alpha CD25C Installation And Servicing Instructions page 36

10.5 FAULT FINDING SOLUTIONS E to K
E
Check pressure tubes are connected
NO
Gas at burner
PCB - X7 connector, is 240 V across terminals 26, 27
F
Check and correct:-
1. Ignition electrode and lead
2. Electrode connections
3. Spark gap and position
4. Connections at ignition generator and PCB connector X7
5. Blocked flue
Is spark generator (T2)
making a clicking noise
G
Check and correct:-
1. Pressure tubes are connected and not blocked
2. If explosive ignition, check wiring to ignition generator is correct
H
Allow to cool. Continuity across thermostat terminals
YES
Air in main heat exchanger, blocked heat exchanger/pipework
or pump not circulating water
I
240V at internal clock
terminals 1 and 2
YES
Continuity across
clock terminals 3 and 4
NO
Internal clock calling for heat
J
Continuity across primary
pressure switch terminals
NO
K
Continuity across DHW
flow switch (hot tap on)
YES
36 V DC at PCB across X8 connector terminals 46, 47
240 V AC at PCB across X5 connector terminals 15, 17
Remove the diverter valve motor, is the brass piston
fully extended (flush with plastic housing)
YES
Diverter valve spindle operating
YES
Check DHW heat exchanger for blockage
Alpha CD25C/28C/35C - Fault Finding
36
Ensure gas is on and purged
NO
Replace PCB
YES
NO
NO 240V at PCB - X1 connector,
terminals 55 and 2
YES
Wiring between clock
and PCB is correct
YES
YES 36 V DC at PCB across
X9 connector terminal 45
and X8 connector terminal 46
NO
Flow rate above 2.5l/min
YES
YES
NO
YES
YES
Adjust gas valve
PCB, X7 connector is 200V ac
across terminals 22, 23 during ignition
NO
NO
YES
Vent air, clear blockage
YES
240V at PCB - X1 connector, terminals 34 and 2
YES
NO
NO
Check mains supply.
Clean mains inlet filter
NO
NO
NO
Check continuity of
motor plug and lead
YES
Check by-pass valve is not stuck open
NO
Replace gas valve
Replace ignition
YES
Replace PCB
Replace overheat thermostat
Replace pump
Wiring between clock
and PCB is correct
YES
Check external controls
are calling for heat
Replace clock
Replace PCB
Replace primary pressure switch
NO
Replace DHW flow switch
Replace PCB
Replace PCB
NO
Replace lead
Replace motor
Replace valve
generator
NO