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
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
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.
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
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).
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!
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!
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