Initially, relay constantly clicking in and out, boiler flaming up and down; then pilot tripped out and once relit kept tripping after 20-25 mins on heating setting. PCB replaced - signs of arcing in and around a relay. No more clicking but pilot problem persisted - definite switch sound as pilot goes out. Thermister (looked manky) and thermocouple replaced; whole system drained and flushed. TRV on one rad replaced with manual valve - now have 2 of these - believe needed to act as sink for getting rid of excess heat in system to prevent boiler overheat. All rads getting red hot. Problem persists, though pilot remains lit for 45mins - 1hr. The only way to stop this is by having all rad TRVs set to max - pilot then stays alight. Been charged £400 so far but still not sorted. Seems to a bonehead like me that the boiler is overheating and a safety switch is cutting the gas supply. Fan working fine, by the way. Any ideas gratefully received!
I had a similar problem without the clicking - I repositioned the thermal cut out switch on the CH flow slightly lower on the pipe to below the pressure switch (the black box with 3 wires coming out). I also reduced the contact area with pipe, and thermal paste on the cut out switch so it's less sensitive. This gave the controls a bit more time to switch off the flames before overheating.
If you can reduce the CH temperature, I think that would be better. But the accessable CH potentiometer reduces burner pressure and not set temperature, so you'll have to work out how to do this.
Dan Rhys
February 2010
Mike, I had the same problem. Apparently the problem is cause by the factory settings the PCB is dispatched with. Originaly when the boiler was manufactured the CH was set to 82 with the boiler overheat fixed at 85. The most recent advice is to reduce the CH temp to 70 giving a larger margin before you reach the cut out. This is in addition to the boiler engineer doing the usual burner presure settings. Everything should then work fine.
Paul
January 2010
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