On 17/01/2021 10:10, 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.

Some/many boilers control the pump, and have a built in overrun timer to
run the pump longer than the main thermostat demands.

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

Yes