Alpha CD24C Installation And Servicing Instructions page 35

10.4 FAULT FINDING SOLUTIONS A to E
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
E
Check pressure tubes are connected
NO
Gas at burner
is 240 V across terminals 26, 27
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
Ensure gas is on and purged
PCB - X7 connector,
NO
Replace PCB
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
YES
Fan jammed or faulty winding
YES
Neon D
NO
NO
Replace PCB
YES
Replace PCB
Replace transformer
Replace pump
YES
YES
NO
YES
NO
Adjust gas valve
Alpha CD24C/32C - Fault Finding
Replace PCB
YES
Replace sensor
YES
Replace fan
Replace PCB
Replace fan
Replace PCB
Replace gas valve
35