Air in system

[surfrider]

I recently drained down the system to replace a number of radiators. A problem has now developed whereby air is being generated or some how being allowed to enter the system.

If the heating only is on there is not a problem, but when the water to the hot water tank is being heated, then I can hear the air going through the boiler.

The boiler has an air vent fitted and I also have an air vent near to the hot water tank in the airing cupboard.

The air seems to end up in the heating system and the only way to get it out is by bleeding one particular radiator.

I would be grateful for any advice as to what is causing this and it there a solution?

 

[ChrisR]

Does water come from all vents?
Turn all off and open motorised valve(s) manually, then vent.
Also bleed pump

 

[surfrider]

I have seen water coming from the vent in the airing cupboad probably after air has been emitted, and I have on occasion heard air coming from the vent on the boiler. I'm quite sure both are working correctly.

Don't think the pump, which is located in the boiler has air in it as the pump is running quietly when the heating is on. Air noise is only there when the boiler is heating both radiators & water.

Something else I've noticed is that the open vent pipe that's over the header tank in the loft actually emits water into the tank. The depth of water is 150mm and ends being fairly hot. Is this normal?

I think I've read that the water level should just cover the bottom of the tank. Can air enter the system via the vent pipe?

If so, is there a solution?

 

[ChrisR]

Is this normal?

No, it's a fault.
Do a search on "pumping over".

If the vents are automatic, close the caps, for now. If manual, keep trying them.