Frost stat problems?

6 Sep 2006
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United Kingdom
Hi - I wonder if anyone can help - my mum lives in a bungalow (circa 1990) She seems to have central heating control probelms which I think might be connected to what I think is a frost-stat. She has a garage sited Worcester Bosch Thermotronic 240 Combi BF&OF? boiler. Close to is what I think is the frost stat - it has a numbered dial on the front - from memory these go up from 5 into the 20's and 30's?... It seems like there is a micro switch in this and when pushed it seems to trip the boiler in some way? When the weather is frosty she seems to have the problem of the heating coming on even if switched of at the timer. She appears to have no thermostat in the house - just thermostatic valves on all radiators. the bunglaow is open plan. I read some where that a pipestat is required to trip the boiler out again once it has fired up to protect itself by frost-stat command? I'm not sure if she has one - how would i know? I also read that newer boilers have frost-stats built in?..

Any advice gratefully received!


Graham Lennard
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I appreciate the frost stat is there to fire up the boiler independent of programme settings but the heating is not meant to come on is it? (all night in some cases) Isn't the boiler meant to come on but then be limited from running by a pipe stat that switches it off once it's warmed up?

The frost stat has its own supply of electric i.e. not through the programmer. This, as you say, fires the boiler to prevent boiler and pipes from freezing (which obviously means in other words the heating comes on). You are also correct that there should be a pipe stat on the return to the boiler set at say 20-30 degree's c to prevent the boiler running up to full temp. as this is just a prevention from frost rather than trying to heat the house up to temp.
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