Can't seem to win with CH

[pompeysprk]

I know the old problem of noisy CH systems has been drawn out time and time agin on here but i have read most of the other threads and have tried most of the solutions to no avail. PROBLEM>>>

I have a vented ch system which seems to get air in it every few weeks thus its quiet noisy . I have flushed, cleaned and inhibited the system twice now .I tried some of the helpfull tips like turning the pumps down and ensuring the header ball c*ck wasn't stuck , checked for leaks ,etc etc. I now seem to have introduced another problem or it may have always been there, now i have turned down the pump speed my boiler seems to be kettling pretty bad, if i turn the speed up the kettling stops but the noise from the air ingress starts to occurr again. Is my only solution to replace the boiler , i have tried turning the boiler to its low (it only has LO, off, high) setting but the output isn't sufficient for the cold snaps wew are having. any advice.

please

[Paul Barker]

On the flow side of the boiler the first T which is the vent pipe tend to be in a negative pressure zone (because the pump is drawing on tha area) so air cannot escape up the open vent. The trick is to make thi T out of one pipe size larger, the sudden expansion of the water a that point allows the air to release. If yours is a 22mm T get a 28mm put in. Kettling is quite normal on cast iron boilers, even from new

-- Paul Barker

[Ed Sirett]

Please describe the exact arrangement of boiler, pump, vent and feed pipework. It may be that you simply have a system that is wrongly/marginally installed.

More or less the only good way for the pipes to be installed is.

The boiler flow pipe goes to vent pipe always upward and in 22mm. The the flow is teed from the vent pipe and very near by has the feed pipe from the header tank teed into it. Then comes the pump.

Such an arrangement has the system pressure under at least the same positive pressure as it is when stopped. Barring a blockage between the vent and feed pipe won't pump over.

Older system with cast iron boilers may have the feed and vent pipes either side of the boiler and the pump pushing water into the boiler. This can lead to a negative pressure in the highest radiators and the induction of air into the circuit.