Central Heating FlowProblems

[John.g]

Sounds good, also inspect pump ports and impeller for any build up.

 

[doitmyself]

As for your other questions, the distance from water level in tank to top of bend in vent pipe is 700mm and water depth in tank when hot is 180mm

They were my questions; but that's not important. The important thing is they are acceptable distances and shouldn't give rise to pumping over.

I agree with John.g that you need a balancing valve in the HW circuit (they are usually fitted on the return).

1. Do you know if the system has been balanced?
2. Do you have TRVs on the rads? If so, turn them all to max and see if you still have the problem.

 

[Mike Mays]

They were my questions; but that's not important. The important thing is they are acceptable distances and shouldn't give rise to pumping over.

I agree with John.g that you need a balancing valve in the HW circuit (they are usually fitted on the return).

1. Do you know if the system has been balanced?
2. Do you have TRVs on the rads? If so, turn them all to max and see if you still have the problem.

Yep, I have TRV's on all the rads and I have tried flat out. There's no problem as far as the CH is concerned so long as the cold feed is twixt vent pipe and air separator BUT, this then introduces the pump over problem which occurs when the lower resistance HW circuit comes in. If it's still a problem after I've checked the pipework is clean and I've moved the cold feed back to its original location then as you and John have suggested, I'll look at fitting a balancing valve. The return from the coil in the HW cylinder is easily accessible.