radiator filling with air/gas - new boiler

[noisypipes]

I had a new Baxi condensing combi boiler fitted 18 months ago and ever since the bathroom radiator has been filling with gas or air (takes about 2 weeks to go cold after bleeding). I've had the company back loads of times but they seem to be at a loss as to what's causing it. Some of their people say it's air getting into the system from a leak - but there is no loss of pressure in the boiler and it is a sealed system. Others say this is impossible and it is "gassing" caused by gunk in the radiators. The system has been power flushed 3 times (first time not done properly) and various inhibitors put in. The radiators are all more than 15 years old. The warranty on the boiler expires soon and I am very concerned that this problem is still ongoing.

Can anyone tell me definitely what is causing it, how we can prove what's causing it and what can be done to fix it....P..L...E..A...S...E........

 

[Bon]

It sounds like there is definitely air getting into your system. The fact it takes 2 weeks to result in a cold radiator will make it even harder to find as it's likely to be very small.

Did they change any of your radiator valves when they put your new boiler in as this would be my first suggestion as to where to look.

If it's never been right, then keep getting them back as they've failed to successfully install it (i.e. the fact it's been 18 months since it was done is irrelevant)

 

[noisypipes]

Thanks for your quick reply Bon. They did replace some of the radiator valves with TRVs but all of these have been checked and replaced again.... there is no obvious leak from any of them. Only the valves and the boiler were changed the rest of the system is original and there was no leak before so, if this is what it is, how might it have been caused? I cannot afford to have all the floorboards up to look for a tiny leakin the pipework - is there any other way to find it? Woudn't you expect the boiler pressure to drop if there was a leak?

 

[Bon]

That's the problem, it won't be an obvious leak if it's taking 2 weeks for the rad to fill with air.

Did you have a sealed system before the combi? Or was it a traditional open-vented system with a small cistern in the loft??

My thinking behind that is that it could be a problem on an existing fitting that has only become apparent since the system was changed from open to closed.

Did they carry out any kind of pressure test on your existing pipework prior to fitting the boiler?

 

[45yearsagasman]

I find it hard to think that air can get into a system that is pressurised above atmospheric pressure!! You should be able to ID what this "gas" is by venting the rad into an inverted container and then applying an ignition source to the container.If it goes POP then you have hydrogen gas forming in your system.Call your installers back.There are chemicals available to prevent "Gassing"