Frost thermostat - boiler running all night - why?

[DaveA]

I have moved to a house with a gas fired central heating system with the boiler in the garage. There is also a frost thermostat in the garage. Presumably the purpose is to prevent the boiler or pipes freezing. My problem is that on frosty nights the boiler seems to run almost continuously and the hot water and bathroom radiator get extremely hot.

Of course there's no radiator in the garage so the frost thermostat doesn't get warmed and cut out. What should cause the boiler to run only intermittently in this situation? Surely it is wasting lots of energy by running all night when all that's needed to avoid frozen pipes is to fire up very occasionally.

Any ideas?

Thanks Dave

[David Hearn]

My boiler manual expressly states: "The frost 'stat should be sited in a cold place but where it can sense heat from the system."

In your case, I suspect that it cannot sense heat from the system and therefore the boiler keeps burning to try and bring the temp up to above the frost temp.

David

[John]

continuously

Get hold of a frost protection pipestat and mount it on the return pipe to the boiler. Wire it in series with the present frost stat such that power from the existing stat goes to the heating system via the Normally closed contact of the pipestat. The pipestat should be set to about 20degrees C so when the boiler is called in it only warms the pipe up to 20 degrees rather than full temperature.

[Christian McArdle]

As well as fixing the frost stat as hinted in the other posts, you should also fix your hot water zoning. If the hot water cylinder gets too hot, it indicates that you have a failed/missing zone valve or thermostat on the hot water circuit.

Christian.

[Tim Mitchell]

In article , Christian McArdle writes

It sounds like gravity fed hot water, in which case there will not be a zone valve or thermostat.

[Christian McArdle]

Not entirely true. Although such systems are usually valveless, a zone valve and thermostat can usually be added to a gravity circulated system, provided the boiler allows it. It's even better if you add a pump as well (in which case the zone valve can be replaced by a check valve).

Christian.

[DaveA]

Thanks for this advice. I believe my frost stat is working correctly but having more thoughly reviewed other posts I am now wondering whether I either haven't got a thermostat on the return pipe or it is faulty. Another job for the weekend!

[Paul King]

Dave, I have exactly the same setup as you - boiler and froststat in garage - and (had) exactly the same symptoms.

I solved it by re-siting the froststat so that it was directly above the C/H pump ( you could achieve similar by siting it above the boiler if the C/H pump isn't in the garage).

Now when the froststat kicks the boiler on, the boiler goes off again when the pump has heated up enough to warm the froststat - job done!

HTH Paul

[DaveA]

Excellent pragmatice advice thanks Paul. I have moved the frost stat directly above the boiler and will monitor the situation next time we have a cold spell.