In an earlier contribution to this discussion,
Dave Plowman wrote:

In article ,
Set Square wrote:
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!)

This will work, but you might have to add a second relay to the pump,
as you'll be feeding volts to it which may then go somewhere else
that they shouldn't, as it were, with the system 'off'. That's what
happened with mine. I never bothered working out exactly why, but
IIRC it caused the system to fire continuously.


I can't see why you'd need a second relay. I drew a circuit diagram before
posting the above, and satisfied myself that, with the single relay as
described, the boiler firing will cause the pump to run but *not*
vice-versa.
--
Cheers,
Set Square
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