water pumping into F&E tank from vent pipe

[Redhotferrari]

Can someone please help with this problem?

I have a standard open vent heating and indirect hot water system, recently I have noticed that when the water is heating up after a few minutes the vent pipe is venting water into the F&E tank. This happens time after time until it reaches the overflow point, then starts to spill water from the overflow.

I have tried a chemical flush on the system including all radiators, one by one. I think the pipework is all clean now!

I have replaced the cylinder stat, thinking this might not be shutting off, but no good.

I am thinking the problem could either be, the pump is knackered or the coil in the cylinder is holed, although the hot water does appear clean when run.

Even after a couple of minutes, the pump is so hot that you cant touch it without burning your hand, could this be ceased, causing the problem?

Please help as this is starting to drive me mad! I am constantly emptying the F&E through the lowest radiator drain off point, which is obviously airated water into my heating system, not good!

 

[JohnD]

Even after a couple of minutes, the pump is so hot that you cant touch it without burning your hand, could this be ceased, causing the problem?

this usually means the pump is not circulating the water. Take the silver screw off the middle, see if the spindle turns; see if you can turn it with a screwdriver. If not it is jammed.

However if the pump is not circulating the water the boiler is likely to get very hot and shut off.

Might also be a closed valve or a blockage. What chemical did you use to clean it?

If you can take a photo of the arrangemnt of pipes showing the pump, three-way elecric valve or similar, feed and vent pipes, someone may spot a probably cause.

Why are you "constantly emptying the F&E through the lowest radiator drain off point"

What is the make and model of your boiler

 

[Redhotferrari]

Picture might be a bit of a problem. The pump, three port valve and vent pipe are all in the correct order, and this has only recently started happening, so dont think its a design fault, the vent pipe has more than the minimum height before going into the F&E.

The boiler is an old Thorn EMI floor standing system boiler.

Used a Plumb Centre own brand for cleaning, left in system for about a week before draining

Reason for emptying F&E is to stop the damn overflow from going each time the water heats up. When I take the level of the F&E back down to its normal level, after about a week of normal usage the tank is back to the overflow due to the constant venting.

Have checked the pump, the center spindle does turn so dont think its that.

Many thanks