Combi losing pressure




I have had an old central heating system converted to a combi, that was working relatively normally, with occ the pressure slowly dropping to the point the boiler would not fire, so I filled the system up again. Today, I have heard loud banging noises coming from the some radiators upstairs, that I presumed was air, I bled the downstairs rads, all air free, but the upstairs were chock full of air!!!!. It took me ages to bleed them, with the boilers pressure up and down like a yoyo, during the bleeding. I eventually bled them, but the pressure on the system is noticably going down. A couple of the rads have some oozing, but no obvious dripping around the connections to the pipework, but would this cause the problems I am having. The rads that ooze water, have done this since the install. Would I be best getting the plumber back that did the conversion. I suspect the rad connections are just not used to having a pressurized system, as the old system had been in around 25-30 years.

Anyone any advice

PS strange, that all the rads before and after the bleeding still got really hot, I thought if rads were full of air they didnt really get that hot.
Sponsored Links
27 Feb 2006
Reaction score
United Kingdom
I have had the same problem on a new install. Even the smallest leak on the rads system seems to drop the pressure on the boiler. Only a small amount of water needs to escape from the sealed system to drop the boiler pressure down to nothing over a short period of time.

One radiator on my system was leaking such a small amount I couldn't even feel it. I only noticed it by rubbing a piece of toilet tissue over the suspect valve. These leaks may also be letting in a small amount of air, although, if water is coming out, air shouldn't be going in.

If it is a new install I would suggest that you get your installer back to check it over. Some installers don't like old radiators and pipework due to these problems, however, is worth a try.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links