Is it safe to wire up a central heating pump to run permanently?
The pump output from my boiler is not working (previous post) and till
a build a circuit to run the pump and have some overrun I just want to
get the system up and running.
The system has a conventional boiler with a 3 port mid position valve,
Trv's on all rads with a by-pass circuit.
As long as there is somewhere to flow it seems to work.
Mine is on permanently when one zone is on - the fan blown hot heaters
do not regulate water flow, but airflow on the fans.
Its a bad idea if you have an 'all TRV' installation as the pump can end
up working against a close set of valves.
In retrospectm, I should have fitted an overall stat somewhere...or some
other form of OR ing of the local room stats to stop the pump when no
demand was called for..
As long as the water has somewhere to go - which it has in your case - there
should be no problem. A mid-position valve is a good bet anyway, because -
unlike 2-port valves - it always has at least one flow path open. Of course,
if the only path open is CH and you have TRVs on all rads which are all
closed, that scuppers that one - but you've got a by-pass, so no worries.
As far as a pump over-run mechanism is concerned, all you need is a pipe
stat with change-over contacts, mounted on the boiler outlet pipe. Connect
Com to the pump, NC to switched live and NO to permanent live. The way, the
pump will always run when the boiler is being told to fire - and will
continue to run after it stops firing until the outlet cools to below the
stat setting. Set the stat to around 80 degC.
Is it a sealed system? And was the pump simply run from the boiler control
If an open system, I'd say you're in danger of pumping over when all the
I'd feel inclined to fit a temporary thermostat in a convenient room with
the TRV there left fully open so the pump doesn't just run all the time.
*If a mute swears, does his mother wash his hands with soap?
Dave Plowman email@example.com London SW
I've had a two speed Myson C/H pump running virtually continuously
since December 1983. That's almost 22 years. My C/H system is a solid
fuel Bont Esse cast iron boiler. There is an air vane on the side of
the boiler to regulate it and that's it. The pump does go off during
the summer for a month or two. If the lounge gets too hot I just turn
the pump off and the heat goes into the H/W cylinder.
The 1983-84 winter here in Aberdeenshire was a bad one and we lost
electricity for nine days. The H/W cylinder turned over a couple of
times. I was ferrying H/W to the neighbours as they were all electric.
I was throwing burning wood out of the window to keep the boiler from
turning over again. It is a real simple system. I must invest in a UPS
to power the pump should we loose electricity again. Hardly seems worth
it for a once in 22 years event.
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