Why can't I get my radiators to bleed?

[RandomMess]

We have an unvented cylinder system (I think) with separate expansion tank.

The 2 upstairs radiators that are last in the line need bleeding as top half is cold. However after the initial hiss of lots of air escaping no more seems to be???

I understood that the heating was under constant pressure or am I wrong and I need to do something else to increase water pressure in the heating system? I waited overnight and got a bit more air out but still lots to go...

@PigletJohn can you help?

have a look in the loft. You are looking for a small water tank, about 600mm x 300mm x 300mm. It would have a large copper pipe rising above it, then hooking down and entering the lid of the tank. Inside the tank will be a ballcock like an old WC cistern.

1. have you got one?

2. is there any water in it?

3. how deep is the water, and how deep is the layer of mud at the bottom (don't stir it up)?

post some photos if you can

Hmmm no water header tank, there’s is a red sealed cylindrical expansion tank that I can get to if really needed and the main tank?

That black water valve is open, well I turned it the other way and no water trickled!

Had it installed nearly 3 years ago.

Photo of main tank

An unvented system won't have a header thank.
What's the pressure reading by the red cylindrical tank? It should be around 1-2bar. If the needle is sitting on 0, you'll need to top up the system.

How do I top up the system if I need to?

Near to the red expansion vessel and pressure gauge, there is typically a silver coloured braided hose with a black isolating valve at each end - something like this: dnwgit7zg7mqr.cloudfront.net/images/141020-UK/800/83963.jpg

If you can find that, turn both black valves and top up the system. If it's cold (off) - try around 1 bar initially. If it's warm, try 1.5 bar. When fully hot, the system will likely need to run betweeen 1.5 and 2 bar.

Ok I’m going into the basement crawl cupboard of doom to have a look!

Not in the cupboard of doom by the expansion tank! Ended up being behind the tumble dryer just below the photo I took, loads more air out but think need to too up again as still not finished

Once you're fully topped up and working again, it's worth keeping an eye on the pressure gauge over the coming weeks. If it drops back down in a week or so, you have a leak or a fault somewhere.

Will do, can’t imagine we do - well sincerely hope not as all new 3 years ago!!

were the radiators new as well?

so much gas is more common with an old open-vented system, hence my wrong guess.

Yes they were and pipes apart from a very little bit could be old... at least we have plumbing cover...

Our system is also 3 years old and we lose more pressure than we should. I've never managed to track down a leak, so the best guess appears to be a faulty pressure relief valve. I'm told this is not uncommon. Whilst it's not an expensive job to replace, I've not bothered and periodically keep our system topped up. It's unlikely to be covered by plumbing cover as it's not a catastrophic failure.

It was more if we have a leaking pipe somewhere tbh!

Sometimes I don’t like being a homeowner!

Stupid question, but I didn't realise that you need to switch the heating off before you bleed the radiators. Have you tried that?

How odd I can bleed mine and on my old combi system when Off or on, just a bit dangerous with the hot water tricking out. It was the water pressure issue, I didn’t realise my new fanglef system could need topping up as thought it was self contained!

It's better for the system to be off when bleeding. With the pump (circulator) running, there is a potential to suck air in through the bleed valve instead of letting air out. Theoretically. I always bleed my radiators with the system running.