In message .com,
Graham writes
The Boiler is some 10 years old, and has developed a intermittent fault
..

Functions normally most of the time, then started to fail to supply
hot water for heating system.....This seems to happen if its been on
for a long period of time .. ie over night with the house stat turned
down (normal would be shut down 1200 till 0730)

When heating has failed -over night- Symptom's are :-

House thermostat demanding heat ,
(Radiators fully cold)
circulation pump running,
Boiler 'gas' fan running
No flame
No green light
No orange light.

This situation will remain so indefinitely

Found to cure problem.

Turning on house hot water tap

Fan remains running
Can here light 'click' from control box (relay operating)
Can hear (primary water circuit) diverter valve operate
Ignition system fires
Gas valve activates
Boiler lights
Green lamp lights
Orange lights

Hot water will run until tap closed .. normal operation .

Close hot tap
Diverter valve operates (can hear)

But is it actually moving far enough to operate the microswitches

Boiler remains lit / re-lights
flame height rises to full then backs off - normal-
Heating functions normally

Till at some point the house thermostat shuts boiler down, then
randomly the heating fails.to re-start when demanded by thermostat.

I have changed the micro-switch on the hot water demand 'detector'
this at first seemed to of cleared the problem .. however this morning
.. heating had failed .. open hot tap and close .. heating operated as
normal and has remained on all day ..

I don't have a circuit for the flame control module,

Why should it be the flame sup cct ? - I thought it worked in CH mode

It could be the thermostatic ctrl board

I only have the
user documentation that came with the appliance..The schematic, only
shows the inter connections. I can only assume its the part that the
water demand sensor feeds that's developed the fault .. may be a
'dry joint' on the board as its seems only to happen after long
periods of use ?.... as the hot water function is 100 p/c reliable all
of the main parts of the boiler are functioning normally .. its got be
a electronic fail ..has anyone got the circuit ?

Sorry for the long post .. but that about describes the problem
Any one seen this problem ?

Tnx - Graham.


--
geoff