hot water pumping back to feed tank

[MGPHOTO]

Hot water is pumping back to the feed tank of my central heating system. A de-aerator has been fitted by a plumber but to no effect. A plumber has also fitted a valve on the feed pipe but that results in the water feeding back up the vent pipe.I have now left the valve open. All radiators have been bled and are ok. It seems that air is still in the system and causing the pressure difference that results in the water pumping back to the feed tank. The pipes make loud banging noises as the water feeds back when the boiler shuts down.

Any help in diagnosing the fault and identifying a solution greatfully appreciated.

 

[HERTS P&D]

Turn your pump down to the next speed setting and see how it goes.

Andy

 

[MGPHOTO]

Have previously tried turning down the pump but no joy.

 

[dcds4]

extend the vent by a foot or so

 

[45yearsagasman]

Pumping over in a previously ok system is almost always caused by a restriction in the system pipework.Use a magnet on the copper pipe to detect the blockage.

 

[MGPHOTO]

The vent pipe has been extended as far as possible and still there is pump over. Looks like I'll have to get the magnet out to see if I can find a blockage.
Thanks for the help

 

[spraggo]

The vent pipe has been extended as far as possible and still there is pump over. Looks like I'll have to get the magnet out to see if I can find a blockage.
Thanks for the help

Check that the pump is fitted corrctly with the arrow pointing AWAY from the feed and expansion pipes.

spraggo