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POSSIBLE CAUSES
Faulty thermistor
Thermistor wiring open circuit
Poor or faulty connections at thermistor or PCB.
N B The central heating mode of the boiler is not affected by a faulty D.H.W. thermistor.
Lock out will only occur during a demand for hot water.
Also note that during the lockout sequence (no burner running); the thermistor will cool if
the tap remains open. This action may result in the thermistor returning to within its normal
operating range. When this occurs the boiler will relight to produce hot water then return to
lockout when the thermistor temperature increases. If the thermistor is subject to the
above conditions then it will not be possible to obtain the full fault code of 10 one second
flashes. This may result in an incorrect fault code being observed.
A Complete fault code must have a 5 second flash at the Start and the End of the
sequence.
FAULT 12
Central Heating Thermistor Failure – (Clip on Type)
5 seconds – twelve 1 second flashes - 5 seconds
If the values of the central heating thermistor are out of range lock out will occur
until values return to operational levels or the faulty thermistor is replaced.
POSSIBLE CAUSES
Faulty thermistor
Thermistor open circuit
Poor or faulty connections at thermistor or PCB
Boilers with serial numbers after 050410747 have the thermistor located on the left hand
side of the primary heat exchanger (to the left of position 11 in the hydraulic circuit diagram
on page 10) Boilers prior to serial numbers 050410747 have the thermistor located on the
flow pipe to the 3 way valve. (Position 4 on the hydraulic circuit diagram on page 10).
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