Central heating thermostat problems?


Postby rennie » Tue Mar 25, 2008 2:06 pm

Any one help?,new ish combi boiler system all working fine then trouble with the central heating not getting hot.Dont use the timer just switch on at the thermostat(which is new-2yrsold-).Allways got hot water at the taps but the heating wouldnt come on despite the thermostat clicking,repeated turning thermostat on/off would sometimes work, problem getting steadilly worse.So I fitted a new thermostat,the heating is now on all the time and only goes off if we turn the timer off.Re-fitted the original thermostat and the problem persists(took photos of the wiring before removing the original so I got it right)heating on all the time unless we turn the system off.Could it be the frost thermostat in the attic?,or the old timer system(which we dont use).Is it a self fix problem or do I need pro. help.Thanks if any one can help. rennie
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Postby htg engineer » Tue Mar 25, 2008 8:35 pm

Heating on all the time ?
Even when the room reaches the temperature set on the stat ?
What about if you turn the thermostat on the boiler down ?
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Postby rennie » Tue Mar 25, 2008 9:37 pm

WHEN THE ROOM REACHES THE TEMP. SET ON THE STAT. THE HEATING REMAINS ON,TO DATE HAVENT TOUCHED THE THERMOSTAT ON THE BOILER ITSELF,ORIGINAL PROBLEM WAS THOUGHT TO BE THE ROOM THERMOSTAT,THE NEW ONE WAS NO BETTER.TROLLING OTHER SITES SUGGESTS THE 3 WAY OR THE MOTORISED VALVE STICKING OPEN.
SPENT A FEW MINUTES OBSERVING THINGS AND IT OFTEN SOUNDS AS THO. THE BOILER WANTS TO FIRE UP BUT DOSENT.CAN MANAGE TECH. WISE CHANGING STATS. ETC. BUT THIS VALVE WOULD BE BEYOND ME FOR MAYBE OBVIOUS REASONS.
rennie
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Postby htg engineer » Wed Mar 26, 2008 11:50 am

If that is the case, then it looks like it is a wiring fault.

Out of curiosity - How do you know the room is at the temperature the stat is set to ? did you use a thermometer ?

Combi boiler's don't have 3 port valves.
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Postby ericmark » Wed Mar 26, 2008 5:16 pm

Frost stat and room stat are only external components on most combi boilers as the name suggests everything else combined within a single box. I would remove the wires to stats at the boiler and see if it still fires up. But I am an electrician and I am skilled enough not to hurt me or the boiler. Not sure if this is something you should be doing? Technically is does have valves and pumps but these are all built into the main box and I would not go into them myself as even if you do find the fault getting parts without Corgi registration is a pain and it is easier to call the repair service man for that make of boiler.
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