Pump not stopping after heating shuts down.

[LondonStone]

Recently I have noticed that when my CH or HW switches off, occasionally the water pump continues going, which gets rather noisy after a while.

It happens about once or twice a week. So not everytime the system stops.

If I turn up one of the thermostats (CH or HW), wait for the motorized valve to open, then reset the thermostat, this pump usually stops a few seconds after the valve shuts, as it should.

I have a Potterton Profile 80 boiler. Two 2 port valves (1 for CH 1 for HW), a honeywell pump and a potterton EP2001 control panel.

It is a sealed system, and the red header tank in the loft is showing 1 bar of pressure.

I had some trapped air in the hot water tank caused when the whole system was badly refilled. But have recently fixed this by bleeding the air vent by the HW valve and the pump.

Could someone explain exactly how the water pump works, so I can figure out why it sometimes keeps on running?

It is currently set on the 2 speed. Should I try running the system on a slower speed and see if the problem reoccurs?

Thanks in advance for your helpful advice.

 

[Gasguru]

Your system is behaving as it should.

The pump will continue to run for a short time after the boiler burner has fired and then shut down. This allows heat within the boiler heat exchanger to be dissipated (preventing nuisance overheat thermostat trips).

The system has apparently been wired correctly ie the pump directly off the boiler, however since you mention a noisy pump the system may have been incorrectly plumbed.

With two 2-port valves you must have a bypass circuit ( preferably an automatic bypass valve) to allow water to be pumped around when both valves have shut (ie heating and hot water satisfied) and the boiler has switched on the pump overrun. Sometimes the bathroom rad is used as a bypass loop.

 

[ACOperson]

The profile has a pump over-run facility where - if properly wired in - it keeps the pump turning after the call for heat has stopped. This is to dissipate heat from the boiler, thereby protecting the heat exchanger from having lots of very hot water sitting in it after it has switched off. It should only over-run for 2 minutes or so.

Have alook at your boiler installation instructions here:

http://www.partsarena.com/baxi/System/index.htm

and you'll see what I mean.

-----------------------------------------------------

Bah, beaten to it by gasguru!

 

[LondonStone]

Thanks guys,

I now have a better understanding of how my system works.

I am confident that the system is wired up correctly, as it's been working perfectly for 3 years.

As far as the plumbing goes, it all seems to be in order, but I'm far from an expert. There haven't been any recent changes or ammendments to it anyway.

Between my pump and the two 2 port valves there is a third branch which has it's own isolation valve (a white peggler tap). I assume this is the bypass circuit you describe.

The peggler valve is fully opened, and the circuit heats up whenever the heating is operating.
I can see where an automatic bypass valve would be preferable, as it would shut off this curcuit when the motorized valves were open right? No point pumping hot water where I don't need it. Next time I have a plumber in I will ask him to fit one.

I still think I have a problem with this bypass circuit, as on the occassions when the motorized vales shut, and the pump continues running, it runs for over 10 minutes, probably longer, but I manually stop the problem before then.

It also makes a pretty ghastly noise, like wind blowing down a chimney, which you can hear in all the house's pipework. It sounds like the pump is pushing water against a large amount of pressure to me.

I'm guessing that the bypass circiut is somehow blocked then?

Anyone know what might have caused it to stop flowing properly?
Or any simple way to clear it?

Thanks again guys!