pump overrun

[stormin7315]

Hi
I have a worcester bosch greenstar 24ri condensing boiler,and was wondering what actually makes the pump overrun when the boiler shuts down.I know it has to do this to get rid of heat in the boiler but what makes it then switch off after a given ammount of time.I realise that it is wired to the boiler.Can you enlighten me please?
Thanks

 

[doitmyself]

It will be controlled by either a timer or a thermostat in the boiler.

 

[gassafe]

Probably a timer, it has a built in over run of about 3 minutes i think.

 

[diamondgas]

PCB will run the fan for 30sec and pump 3mins - Some boilers use the flow temperature sensors to determine whether to overrun or not others have an overrun stat that registers the flow temp and will run the pump until the flow temp drops. I think most manufacturers are going for the pre-set timers nowerdays?

 

[stormin7315]

Hi guys
Thanks very much for your quick responses.Pump overrun now a bit clearer to me now.