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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Plumbing Questions >> Pumping over https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1162570063 Message started by londonman on Nov 3^rd, 2006, 4:07pm

Title: Pumping over
Post by londonman on Nov 3^rd, 2006, 4:07pm

Just discovered that my CH system pumps over in spurts into the expansion tank. Not continuously but enough to warrant attention. The easiest option for me is to extend the upsided-down J ...but..will this work? How high does it need to go as the roof apex is very, very low. ....probably less than a metre above the expansion tank water level.

The boiler is an elderly Worcester PJ26-32. There are four pipe connections at the back. CH/HW flow is top left and flows into the pump. Bottom left is for the main CH/HW return. Top right is the overflow/expansion pipe and bottom right is the feed pipe from the expansion tank. So my understanding is that it is on the correct side of things so why does it pump over?

Title: Re: Pumping over
Post by thescruff on Nov 3^rd, 2006, 11:44pm

Cold feed is partially scalled or blocked where it joins the boiler.

Drain a small quantity of water from a radiator and check if the header tank is re-filling.

Title: Re: Pumping over
Post by londonman on Nov 4^th, 2006, 11:53am

Checked and water flows freely from header tank into boiler.

Title: Re: Pumping over
Post by CWatters on Nov 4^th, 2006, 5:31pm

It's not boiling the water is it?

Title: Re: Pumping over
Post by JerryD on Nov 4^th, 2006, 10:45pm

I've seen this before in lofts where there is low headroom and it happened when the pump turned off. There was a slight surge and about a cupfull of water pumped over.

We turned the pump down from 3 to 2 and the pumping over stopped and fortunately the heating system still functioned properly on setting 2.

Title: Re: Pumping over
Post by londonman on Nov 6^th, 2006, 1:56pm

No, it's not boiling over. Sounds more like the scenario Jerry had. Guess I'll just bite the bullet and extend the ventpipe as high as I can and just hope that it stops. If I turn the pump down then some of the rads at the furthest end of the runs don't get hot.

Many thanks for the suggestions.

Title: Re: Pumping over
Post by JerryD on Nov 6^th, 2006, 8:18pm

If it is just a short surge from the pump turning off then extending the vent pipe will definately help as the 'surge' water' will have to travel further before exiting the vent pipe.

If you are really stuck for headroom then increase the size of the vent pipe from 22mm (which I assume it is) to say 28mm or bigger as this will have the capacity to contain more of the surge water making it less likely to pump out.

In EXTREME cases you could even construct a manifold from approximately the header tank water level and have several vent pipes!

Anything to be able to 'contain' the surge water for the few seconds it is....er.......surging?

You know what I mean ;D

Title: Re: Pumping over
Post by londonman on Nov 10^th, 2006, 1:27pm

Thanks Jerry and others...some cracking ideas there. I've extended the existing pipe and gained about an extra 600mm head and that seems to have cured the problem.