Technical data
23
Prior to fault finding, check :
Inlet gas pressure = 20 mbar
Electrical supply = 240 V - 50 Hz
Central heating system is pressurised at 1 - 1,5 bar.
Overheat thermostat on RHS of heat exchanger has
not tripped reset if necessary.
Carry out electrical system checks i.e. earth continu-
ity, resistance to earth, short circuit and polarity with
a suitable meter.
Note : these must be repeated after any servicing or
fault finding. Ensure that all external controls are cor-
rectly wired and calling for heat.
The fault finding charts will enable the majority of faults
to be diagnosed. To use the charts effectively, it is
necessary to determine exactly which aspects of the
boiler are working correctly and which are not.
For example:
If the domestic hot water works but the heating
doesn’t, refer to chart No. 1.
If heating works correctly but the hot water doesn’t,
refer to chart No. 2.
IMPORTANT: Always adopt a logical, step by step pro-
cedure starting at the beginning of the appropriate
fault finding chart.
WARNING. Always isolate the boiler from the electri-
cal supply before carrying out any electrical replace-
ment work.
Always check for gas soundness after any service
work.
NO CENTRAL HEATING
CHART 1
Replace main pcb
Replace clock
Refer to chart n°3
Refer to chart n°4
Does fan run ?
Does pump run ?
Internal control
(clock)
External controls
(if fitted)
Remove leaos from boiler
thermistor. Check its
resistance according to
thermistor value table.
Is thermistor ok ?
Short out external controls
connection on top of
reversing valve. Does
burner fire ?
Rectify wiring
operation faults on
external controls
Is wiring between
clock and pcb
connection cn7 ok ?
Replace thermistor
Is clock calling for
heat ?
Is there
continuity across
terminals 3 and 4
of clock ?
Replace
main pcb
Turn ch temp. control to
max. does burner fire ?
NO
NO
NO
NO
NO
NO
YES
NO
YES
YES
YES
YES
YES
YES
Is short selector lever on
front of reversing valve in
right hand position ?
Does burner fire when
a hot tap is opened ?
Refer to chart n°2
YES
YES
YES
SERVICING INSTRUCTIONS
FAULT FINDING
YES
Move to right
NO