Combi losing pressure

[chesketh]

Hi

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.

 

[incdesign]

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.