Air in the central heating - Help!

Hi, I'd be really grateful of some advice on solving a problem with our central heating system. We've noticed that it keeps getting air in the system which is leading us to believe that we have a leak somewhere.

It's a gravity fed system with all exposed pipes through the whole property, so we've been round the whole place checking for leaks - nothing!

The air seems to be in one rad only which is the bathroom one and needs significant bleeding every couple of weeks.

Given that we've checked everywhere for leaks, including the loft, we can only assume that it's the primary coil in the H/W cylinder that's sprung a leak? although there is no sign of brown or debris in the hot water. We don't think the boilers at fault either as presumably you'd be able to hear the water dripping on the burner if the jacket was leaking?

Any thoughts or suggestions would be gratefully received.

Also, if there is a possibility that it could be the H/W water cylinder ( Which is only about 6 yrs old), is there some sort of dye or tracer product on the market that can be added to the header tank to see if it comes out in the hot water tap?

Hello there,

I can empathize with you here. I've had a few jobs in the past which drove me bonkers with this kind of thing.

In my experience (11 years) i've never known the coil to go on an indirect cylinder - anything is possible though! It tended to be in properties with lots of unsupported, horizontally running pipes. I'd fill the system up, turn the boiler on and you could hear the pipes banging and clunking with all the air in the system. I had the same issues, a rad needed bleeding every so many weeks, and it took forever to bleed. In the end the only way i could remedy the problem was by pulling out the thermistor in the heat exchanger on the boiler and allow it over-heat until i could hear the water boiling in the pipes, the increased heat forces the latent air pockets out of the system into the header tank. It's not advisable though, if you don't time it right and leave it too long you can split the heat exchanger - which will mean a new boiler. I realise this is going too be the professional, simple fix solution for you, but unless the cylinder is leaking, i think it's going to be a tough one. To my knowledge there are no dyes on the market for a such things.

If your system has no inhibitor and as you say the water is brown, it may not be air that you are bleeding, but hydrogen gas, from the crud in the system.
It is possible to ignite this gas as it comes out of the bleeder. I am not suggeesting that you try this