Boiler Frost Stat


25 Sep 2013
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United Kingdom
I have a problem with me boiler.
It is reasonably new and work fine when hot water and central heating are operated but the problem seems to be when the Frost Stat is operated.

when I set this to a temperature above the ambient temperature and set the temp on the pipe stat above that then the boiler Pump switches on but the gas does not fire - which means that it stays on for a long old time until i use the central heating/hot water.

It is alright now but come winter I think its going to be a problem.

My questions are
is this solely a fault with the frost stat ?
the connections ?
could it be the boiler itself ?

As it's under guarantee (the boiler that is) I would appreciate if anyone knows what the process is - as i assume Mr Worcester Bosch would charge a hefty wedge if it is only the frost stat and connections - but not a penny if the boiler, and Mr independent would give a more reasonable price but may not be able to do any guarantee work on the boiler?
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Exact boiler model would help, as some modern boilers have on board frost protection. A description of your system controls, eg zone valves etc would also help. It sounds like a wiring issue, as the boiler should fire.
Boiler is a worcester bosch 30cdi combi - i believe that there is also on board frost protection from the gumpf that cam with boiler.
Its located in the attic - so there is an external frost stat and pipe stat as I believe that boiler frost protection is for internal pipework only.

If it were only the external frost stat I feel pretty confident i can change this - but not the wiring into the boiler (though i cant think that that would be wrong as there wasnt this problem last winter)
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The frost stat should switch the boiler on to heat up.
That is the point. So it isn't wired right.

Modern gas boilers usually come with frost protection built in.There isn't any need for external controls.
So wiring looks to be at fault.
Can anyone explain why the pump comes on but not the gas lighting ?
had someone round from WB, and wiring is ok. Though he didn't think there was a need for a frost stat given that piping was not that long and far from the boiler. Apparently a frost stat runs the circulating pump only on this model and that would kick in the frost stat in the boiler etc etc.
Wiring is fine, but there still is an issue as at the end of the day the circulating pump is coming on and staying on. I have to set the machine off to stop it. I was wondering if the daily pump run (to stop it seizing when CH not used) could be staying on ? Does that sound like a possible cause?

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