Problem with central heating boiler...

[Joker]

Have a water/central heating boiler in the garage, looks like theres a frost stat on it and we have a timer in the living rom with radiater stats on 4 of the radiators. The pressure when cold is between 1 and 1.5.

When the heating is off the boiler starts up for 60 seconds and then stops, it does this 24 hours a day. However, its recently started doing this every

20 minutes or so and starts and stops for 30 seconds. I can hear it start when im in the house and more so at nights when in bed. When the heating is on it works fine however the last week theres a huge "clunk" in the pipes when it turns off.

Is the above normal ?

thanks

[G8PSZ]

Not a heat ing expert, however have a similar system albeit not a pressurised one, in ours the frost stat in the garage overides all programming so as to protect the boiler, when it is particularily cold ours fires up & of course then has to sink the excess heat into the system resulting in rapid heating of a cold rad system, we get clunks due to rapid expansion followed by cooling as there isn't a contant flow under those circumstances.

Chris

[fred]

In article , Joker writes

See thread for a discussion:

1a7938/

Last post, courtesy of Adam Wadsworth, seems to give the answer, a pipe stat is required as part of a proper design to overcome excessive cycling:

"Just fitted a Honeywell frost stat today. The instructions said to wire a pipe stat (set at 25 deg) on the return pipe in series with the Honeywell stat."

Is there a pipe stat?

[Joker]

Thanks for the info, just had a look at there is no Pipe stat fitted, however the heating doesnt actually heat up as the boiler only runs for between 30 and 60 seconds, what temperature would the water be in the pipes and if the pipe stat was set at that temperature it would just stop the boiler running straight away, is that correct ?

[fred]

In article , Joker writes

I've not done this as my boiler is inside so the following involves a bit of speculation.

Is your frost stat in free air in the garage? If so, it will fire the boiler if just the ambient air is below say 4degC which may be unnecessary. If this is combined with a pipe stat (also in the garage, on the return pipe near the boiler) it will only fire the boiler when the air is below 4 and the water temp is below say 20. I'm guessing that the thermal mass of the water in the pipe would mean that it would stay warmer for longer that 20 mins, increasing the off time. The pipes should be insulated too.

The 60s run doesn't sound too wrong as there is no heating loop to heat up. Your heating circuit will have a bypass valve which returns flow water to the return side when there is no heating demand [1] meaning the return flow heats up quickly and shuts the boiler down, until the next time. Is the return pipe hot when the boiler shuts down?

[1] There must be one as the boiler would lock out if fired without some flow through the boiler.

[Joker]

----- Original Message ----- From: "fred" Newsgroups: free.uk.diy.home Sent: Saturday, March 13, 2010 7:33 PM Subject: Re: Problem with central heating boiler...

The frost stat is screwed to a black plastic box thats inturn screwed to a brick wall, it is pretty much open to free air yes.

If so, it will fire the

All the piepes are insulated in the garage to within like 12" of the boiler.

Its just done a 60s cycle now and feeling the return pipe at the boiler its only just lukewarm.

[ARWadsworth]

Well it is warm enough to try disconnecting the frost stat and see if that is the problem

What boiler is it?

Adam