In an earlier contribution to this discussion,
Malcolm H wrote:

I have a Glow-worm Fuelsaver 40-50 conventional flue boiler which was
installed in 1984.

Everything works fine except that the central heating circulating
pump stops running as soon as the room thermostat reaches the desired
temperature. This results in some noisy bubbling from the boiler as
it overheats for a short time after the room thermostat switches the
pump and boiler off.

Does anybody know if this boiler was designed to have a pump overrun
feature to avoid this problem?

If the boiler was not designed to have a pump overrun feature is
there a control available which can be added retrospectively. e.g. is
there a timed control available which will allow the pump to run for
a short time after each switch off?

TIA


I don't know whether the boiler has a built-in pump over-run facility - but
being 1984 vintage, probably doesn't.

In think that in your position, I would implement my own - using a mains
relay and a pipe stat. Connect the coil of the relay to the boiler switched
live. Connect the relay contacts to a permanent live and to the pump.
Connect the pipe stat contacts in parallel with the relay contacts. Install
the pipe stat on the boiler flow pipe and set it a similar temperature to
the boiler's own stat (a bit of experimentation may be required!)

The pump will then run whenever the boiler is firing *and* whenever the
boiler outlet temperature is above the pipe stat setting. This is, in
effect, what a built-in over-run stat would do - and is better than an
arbitrary time delay.
--
Cheers,
Set Square
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