pump overun

[acslad]

past acs . was easier then i thought.
can i ask one thing. i understand how pump overun works on combi. however on a s or y plan with a boiler wired for pump overun how does the pump know when to stop running since there's no stat? does the pcb have some kind of clock timed for 5 mins to run pump after demand finished? thanks

 

[gas4you]

Yes, more often than not if it is non-adjustable it will be 6 mins.

Most decent new boilers can be individually set by the installer for the length of over run.

Vaillants come set at 5 mins, but I usually change this to 8-10 mins, as the HE's on these don't like heat

 

[acslad]

thanks. if it fails ie pump not switching off i guess its either the motor valve sticking or the timer chip gone (new pcb)??

 

[ChrisR]

however on a s or y plan with a boiler wired for pump overun how does the pump know when to stop running since there's no stat?
Does the pcb have some kind of clock timed for 5 mins to run pump after demand finished? thanks

On older boilers there's a separate stat
I don't think I've seen a timer chip on any boiler. All pcbs these days have clocks in the processor so they don't need one.
Though I expect they time the overrun, it's possible that some will also look at the temperature sensor, and keep the pump running if things are still hot.

 

[acslad]

so it would be new pcb on the newer boilers to replace clock on processor?

 

[namsag]

Older boilers usually had the pump overun stat built into the main boiler stat using the one phial.
Some Servowarm elites had a pump over run board as did some thorn olympics.
Apollos had a seperate disc that sensed temp within boiler casing