In an earlier contribution to this discussion,
pollocmc wrote:

Why do the think that the boiler stat is faulty

No good reason other than following the fault finding diagram has a
branch that suggests that you can have an operational (ie controls
temperature) thermostat but the pump does not overrun. The solution
they give for this is to replace the thermostat.

Yes, but the fault-finding chart assumes that it has been installed
correctly and has subsequently gone wrong. It sounds as if yours has *never*
worked properly. As Ed has suggested, the pump is probably connected to the
switched live and not to the specific pump terminals.

As I said earlier, the boiler needs a switched live *and* a permanent live.
Without a permanent live, pump over-run won't work - because the pump needs
a source of supply whenever the boiler demand has been removed but the
boiler is still too hot. So check *all* the wiring.
--
Cheers,
Set Square
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