On 17 Jan 2021 at 20:40:34 GMT, "Roger Mills" wrote:

On 17/01/2021 09:47, RJH wrote:
My Ideal Logic boiler goes into 'pump overrun' on occasion while the
thermostat is calling for heat. It goes into overrun, then purge, when the
temperature's reached as part of the normal cycle, but I've only just
noticed
this while it's actually heating.

Seems odd to me - if the boiler is trying to 'spread heat' why does it get
so
hot in the first place?


I don't quite understand what you are saying. How are you detecting that
the pump is over-running?

Firstly by sound - I noticed it had stopped 'firing' while the room stat was
calling for heat. Confirmed by the on-boiler display.

Which thermostat is calling for heat - the
boiler stat or the room stat? Is the boiler controlling the pump?

The room stat controls the boiler. The boiler controls the pump. I don't know
the boiler's relationship with the pump, though.


By definition, pump over-run only occurs when the boiler is *not*
firing, but has has some residual heat which needs to be dissipated to
prevent it overheating. [The metal heat exchanger will be a lot hotter
than the water in it, and will continue to heat the water in it if there
is no flow - possibly to the point where the over-heat cutout trips].

Yes, that's what I'm asking. It would make more sense to me the throttle back
the gas in the first place, rather than let it get hot to the point that it
needs to cool down by pumping the hot water away.

--
Cheers, Rob