Central Heating Boiler Constantly Running Problem

by Editor on May 20, 2013

Q- Hi, I’ve discovered the other day that an oil boiler was running even though heat and hot water turned off at programmer. I thought it was the timer and i replaced it but lady said problem remained. I have tested the 2 valves grey and orange wires and not closed, have tested cylinder stat and ok. The system has stopped calling for heat when off at the timer. Any idea as to what was or is the problem?

A- Could it be a frost stat giving a permanent feed to boiler?

Q- Thanks for reply. My oil boiler and burner is in my garage and i have not seen any frost stat. The stat on the boiler is the normal one which has the limit part on its left and the adjust part on the right both inside the cover leaving only a reset button and temp wheel on the top when the cover is on. Something overruled the programmer yet everything is now working but the problem may return. When heating and/or hot water is selected does the signal go first from the programmer to the wall stats (in the case of heating) or the cylinder stat (in the case of hot water), and from them to the respective motorised valve? I have tested the cylinder stat (good) but did not test the wall stats. Can a faulty wall stat allow power to a motorised valve to start the boiler?

A– The signal to bring the boiler on is normally wired: prog>stat>valve>boiler/pump. Yes, a faulty stat could allow a feed to the boiler but the prog would need to be ‘on’.   You could check the wiring diagram at- https://www.electriciansblog.co.uk/2012/02/s-plan-twin-zone-central-heating-system-electrical-control-connections-and-wiring-diagram/ to see if your central heating wiring connections are good.

I hope this was useful.


{ 1 comment… read it below or add one }

Paul Radford December 14, 2014 at 10:26

Could be a sticking switch in one of the valves had this before, when you looked at it you might of released it. Or internal frost stat within boiler.

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