On 17 Jan 2021 at 10:10:49 GMT, "The Natural Philosopher"
wrote:

On 17/01/2021 09:59, alan_m 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 would expect the pump to run continuously whilst the room thermostat
is calling for heat.

I would expect the pump to be running (overrun) when the call for heat
has been met and the boiler has just stopped firing. If the pump stopped
immediately the static water in the heat exchanger would get too hot
because it would be still heated due to boiler components in the heating
path (heat exchanger etc.) still being hot.Â* A bit like turning off an
oven and the food still cooking until the oven cools down after a period
of time.

The pump is controlled by main thermostat. The boiler firing is *also*
controlled by water circulation temperature.

OK, thanks both, I think I get it! So it's not a problem then.

--
Cheers, Rob