DIY Doctor UK DIY Forums

I've had a plumber flush through my 20 year old oil fired central heating system [which has always been reliable] & refill with inhibitor. There is a lot of 'rushing' 'running' 'pouring' water noises sometimes now, around the pump/valve area, when the system is working. It sounds like air to me. The plumber [local, reliable?] has come back, scratched his head & walked away trying to tell me it's normal admitting he has no idea what's causing the noises!
I do have a 10 bar vent device fitted beside the cylinder, which appears to be working; I took it apart & cleaned it, there is an occasional slight hiss as if some air is coming out. The radiators are bled regularly & there is no air in them. I'm a bit stumped; any ideas please as to what may be wrong?

steve1000,
If the pump is feeding downwards from a vertical pipedrop there may well be slug of air in the system. Try turning the pump speed up and see if this clears the problem.
end

It's air, the system has been drained and refilled - try venting pump. make sure auto airvents are open and bleed radiators every couple of days - it will clear eventually.

htg