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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3767
Experience:  Heating and Controls engineer
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Hi, Followed a link to here so apologies if not your area.

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Hi, Followed a link to here so apologies if not your area. Our Halstead Quattro Gold gas boiler has developed a fault which means it will only run when it decides to within its timed period. Thermostat calls for heat & clock is "on", boiler will start & run normally, but then stop as if thermostat says it is satisfied although it isn't and there is power live on the demand cable as there should be. It then won't start for a long time, regardless of how much the temperature falls and starts on its own for no obvious reason. DHW side works normally and sometimes the central heating will continue for a while after use. Fault charts point to Driver PCB, but this has been changed to no effect, as have thermistors. May be just an illusion but radiators do seem hotter when it is running. 3 gas engineers have now left baffled, and its getting colder. Any pointers gratefully recieved
Can you turn your heating down to 1/4 and tell me how it performs.
I am wondering if you have a faulty overheat thermostat and it is tripping too low?
Customer: replied 4 years ago.

Boiler ran as normal then cut out as before, but radiators never got as hot as previously. Tried turning temperature control up again, but boiler did not cut in again.

It definitely sounds like a faulty overheat thermostat.
Are you able to swap this yourself - or get someone else to do it for you.
Andrew Smith and other HVAC Specialists are ready to help you
Customer: replied 4 years ago.

Just so you know, fault was short circuit in one of the microswitches on top of diverter valve, & unlikely you would diagnose that easily at distance . Sorry couldn't reply earlier but broadband also went off.

Not a problem - thanks for letting me know