CH Pumping Over

With our pump on 1 everything is fine, if I put it on two, then it
starts to pump over.
The expansion tank is about 2m above the pump and hot water cylinder,
the expansion pipe goes up a further 0.5m or so above the tank to reduce
the problem but...
Why does it happen, what can one do, can one put a constriction in the
expansion pipe to reduce the effect?
Thanks
Reply to
John
cylinder,
It very much depends on the layout of your CH system. If the 'push' side of your pump precedes the tee that the expansion pipe comes from, then there will be positive pressure tending to pump over. A cure can sometimes be effected by reversing the pump so the water flows in the opposite direction. Many years ago pumps were always installed on the 'return' side of the system next to the boiler so that they ran about 10 deg C lower and lasted longer, however modern practice it to put them on the flow side. My last house had a 'trombone' on the expansion pipe running up to the apex of the roof then down to the tank for this reason.
AWEM
AWEM
Reply to
Andrew Mawson
In article , Andrew Mawson writes
Yes I added a trombone a few years ago, but it still seems that with the pump on 2 it will try and pump over.
Reply to
John
In an earlier contribution to this discussion,
Have a close look at how the vent and fill pipes are tee'd into the main flow pipe. They should both be on the 'suck' side of the pump, and no more than 6" (150mm) apart. If they are on the wrong side of the pump (or one each side!) or too far apart, there can be a pressure differential between them which causes water to flow up the vent pipe and back down the fill pipe.
Reply to
Roger Mills
The cold feed pipe from the F&E tank should be nearest to the pump on the suction side. The two tees should ideally be next to each other on the flow pipe.
What type of boiler is on the system?
Reply to
Doctor Drivel
In article , Doctor Drivel writes
The two pipes are within a few inches of each other on the suction side of the pump. I think the feed is after the expansion - I need to go up into the loft to double check. The expansion is 22mm and the feed is 15mm (if I have got them the right way round.
Boiler is an old potterton non-condensing, non-combi just heats the water type!
Reply to
John
In an earlier contribution to this discussion,
Strange - there's no obvious reason why it should pump over. What size is the main flow pipe in the region where the vent and feed pipes are tee'd in? How much above the water level in the F&E tank is the highest point in the up-and-over vent pipe? Do you have room to increase its height?
Reply to
Roger Mills
In article , Roger Mills writes
The pipes around the cylinder (where the pump is located) are all 22mm.
I will need to check but the trombone I made gives about 0.5m above the header tank level.
Reply to
John

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