DIY Doctor

possible thermostat problem

Postby stormin99 » Wed Mar 31, 2010 8:00 pm

I have an old style analogue Honeywell room stat that appears to be stuck at 62 degrees or thereabouts...When switching the central heating on it runs for about 15mins(no more)then switches off leaving the water to get hotter until the point that the tank then overflows!
Would I be right in thinking I need to replace the room stat and possibly the thermostat within the boiler....or is it a little less disastrous than that?
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Postby oldie » Thu Apr 08, 2010 8:59 am

Sounds a bit like a problem with the boiler stat, possibly exacerbated by poor circulation through the system.

Hot water coming out of boiler should not exceed 80º.

Many boilers are set to a max of about 70º, especially those heating a hot water cylinder, as this is more than sufficient to heat the water up to 60º and avoid any Legionaires disease type problems.

Also remember if you heat hot water coming out of a tap much above 60º you are incresing the risk of scalding.

This is why the authorities are trying to introduce TMVs (thermostatic mixing valves) in the water supply to hot taps to keep the maximum outlet temperature below about 46º.
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Postby sparx » Mon Apr 12, 2010 4:48 pm

hi, have read this several times and am confused!
you say the room stat brings the boiler on for a while then goes off but water in the TANK? gets hotter,, not sure what system you have but the room stat does not control the hot water, there will be a tank stat unless old gravity hot water set up when the final temp will be controled by the boiler stat.
More info. ref motorised valves/pumps/stats/time clocks etc.
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