Alpha CD25C Installation And Servicing Instructions page 35

10.4 FAULT FINDING SOLUTIONS A to D
A
240 V ac at:-
1. Main terminals L and N
2. Main terminal fuse
PCB - X1 connector, terminals 55, N
3.
NO
PCB fuse
4.
240 V ac at:-
B
YES
Pump
1.
PCB - X6 connector, terminals 18, 19
2.
C
1.
Check and correct connections/wiring at sensor and PCB
2.
DHW/Primary temp. sensor faulty. Cold resistance approx.
12-14 k ohms (resistance reduces with increase in temp.
i.e. when hot, resistance is approximately 3 k ohms)
D
1.
Check and correct:-
1. Electrical connections
2. Restriction in flue
2. Fan connections correct at fan and PCB connector X12
PCB connector, is 36 V dc across terminals 39 and 37 or 38
NO
Boiler cycles on and off
3.
In CH mode. PCB - X5 connector, is 240 V across terminals 15, 16
In DHW mode. PCB - X5 connector, is 240 V across terminals 15, 17
Remove the motor from the diverter valve.
Does the piston move in and out when
operating the boiler between CH and DHW
Is diverter valve spindle sticking
NO
Check electrical supply
NO
Replace fuse
NO
Check wiring
Replace fuse
Neon D illuminated contiuously
Is 240 V ac across
PCB X4 connector terminals 11,12
Is 26 V ac across
PCB X11 connector terminals 40,41
NO
3.
Neon A and B flashing
at the same time
YES
YES
YES
NO
YES
illuminated continuously
NO
YES
NO
NO
If pump jammed, release
Replace PCB
DHW temperature sensor faulty
i.e. heating OK. Hot water operates
but does not modulate
Check resistance throughout
the range from cold to hot
Primary temperature sensor faulty
i.e. no heating or hot water
Fan runs at maximum speed
YES
(BUT)
Is dc volts at PCB, X12 connector:-
across terminals 35 and 37 - 34 V dc
across terminals 36 and 37 - 4 V dc
NO
YES
Fan jammed or faulty winding
NO
YES
NO
Check continuity of plug and lead
Ensure by-pass slot is in horizontal position
and that the valve is not stuck open
Neon D
NO
NO
YES
Replace transformer
YES
YES
YES
YES
YES
NO
Replace diverter valve
Alpha CD25C/28C/35C - Fault Finding
Replace PCB
Replace PCB
Replace PCB
Replace pump
Replace sensor
Replace fan
Replace PCB
Replace fan
Replace PCB
Replace PCB
Replace motor
Replace lead
35