CH/HW pump running longer than expected

[Pnb]

Hi, hoping someone can help me out with a query I have with my CH/HW system pump.

My system is a fully pumped system I believe but the pump will often keep on running for up to an hour after the CH and HW has switched off at the main controller. It's more noticeable when having a shower just before the HW switches off at 10pm and the pump will still be running up until almost 11pm.

Is this normal for a Fully pumped system as I thought the pump would only run when the controller was calling for HW or CH or possibly for just a couple of minutes after they had switched off to disperse the heat but not the length of time that it is currently running without any demand.

Hope someone with more knowledge can give me some advice! Thanks.

 

[dilalio]

What boiler?
What system? Y or S plan?

Sticking microswitch on MCV would result in boiler firing as well as pump running so it would appear to be the pump overrun stat/timer module on boiler.

 

[Pnb]

Boiler is a Worcester Greenstar Ri and I believe it to be a S plan system as I have two separate two way zone valves, one for CH and one for HW instead of a single 3 way valve.

 

[dilalio]

You need to test with a multimeter or employ someone to do it for you.
I'd be testing the circuit that provides live to the pump.

 

[McCombi]

Is the pump wired direct to boiler rather than the wiring centre? If not it should be.

Also, is there an automatic bypass valve on the flow pipe from boiler before the 2 port valves, and pipes back into return pipe to boiler?

If not, pump and fan will stay in for ages as boiler can't get rid of heat from heat exchanger after a demand.

This will shorten lifespan of boiler if not fitted

 

[Pnb]

Thanks for your help so far.

McCombi, im hoping you may have suggested the solution, after looking at my pipework I think I do have a bypass pipe back to the boiler from the pump which has a tap on it (marked with a red circle on pic 2), this tap is currently closed allowing nothing to flow back, do you think this should be open?

Hopefully the images below will show the pipework in my airing cupboard ok, the close up is of the pipework at the top of the main image, i assume the larger diameter pipe coming up through the floorboards is the supply from the boiler and the smaller diameter one next to it is the return supply to the boiler for the bypass.

 

[McCombi]

Yes crack it open slightly. It should help to take residual heat away from boiler

Ahoukd be an automatic bypass type but a gate valve is better than nothing

 

[Pnb]

Thanks McCombi, seems to have sorted it, earlier in this evening it took 20 mins for the pump to stop running after i turned off the HW timer and just tried it again now whilst it was calling for HW and the pump only overran for 3 mins and switched off.

Once again thanks for all your help.