Air in central heating and overflowing

[Rob Nicholson]

There is something rather unwell with my heating system but it's never been quite right since I bought this house. Current problem is the radiator nearest the boiler and pump (which is upstairs in the back bedroom) is continually filling with air. Bleed it and it goes hot instantly but will be full of air in a couple of days. Air and bubbling can also be heard in and around the boiler/pump. Additionally, there is a little overflow pipe sticking out of the wall just above the boiler that is continually dripping. I'm not sure how long it's been dripping for. It drips whether the central heating is on or off.

Now some history:

The pump packed up a couple of years ago and the plumber who fixed it said that whoever had installed the central heating got some pipe work wrong around the pump area which meant it would be pulling air into the system. Even if it was, does it explain why suddenly more air is getting in.

I recently drained the system twice in order to remove and decorate behind a radiator in the bedroom. This radiator is working fine. However, some quirks here: firstly, the water only dribbled out of the release valve in the cellar (the lowest point). Secondly, upon refilling it took an awfully long time for the radiators to start getting hot again. The thermostat on the boiler was set to very low - it's currently on medium. Could there be a blockage somewhere?

There is a very slight weeping of one of the radiators downstairs - so slight that the water evaporate before it drips. It's been sealed with something I got from B&Q - a sort of silicon sealant stuff. Not sure how effective it is though. Could a slight air leak like this cause a radiator at the other end of the house to fill with air?

The radiator down in the cellar is damaged but as I don't particularly want to heat the cellar, it's turned off at both ends.

Any ideas? I suspect I need a good plumber in here - whilst I understand the principles of the thing, diagnosing something like this is a lot more difficult.

Thanks, Rob.

[Ed Sirett]

I expect that this system is open vented and the pipe above the boiler is the over flow for the little (10 litre) F&E cistern.

A few photos of the pump / boiler area would help a lot.

The pipework need fixing to stop the air entering and before other problems get too serious.

The valve in the cellar is a drain point - the washers often weld themselves in place and opening the valve only allows water out from the middle of the washer.

[Alan]

In message , Rob Nicholson wrote

One possibility is that the pump is running too fast. It probably has three speed settings - reduce the speed. You may have to re-balance the system.

You may have an airlock in the pipes feeding that radiator. To clear try turning off all the radiators except the problem one.

[Rob Nicholson]

I'll snap a dig photo later and post it. Need to move out a lot of junk from the cupboard :-)

Suspected that - will order and replace the two faulty radiators. I was putting it off as the weeping on is a large one in the lounge, biggest in the house :-(

Okay, won't worry about that too much then.

Cheers, Rob.

[Rob Nicholson]

Will do - later...

[David W.E. Roberts]

When you drained the system, did you run it for a while with a flushing compound then drain it again then refill with an inhibitor such as Fernox?

A long time ago I had a problem with one radiator constantly filling up with air (or other gass(es) ) and was advised that this could be the result of corrosion of the inside of the radiators. This gets worse when you add fresh water - apparently the water can stabilise a little after time.

I ran with the flushing compounr, flushed the system, then added fernox and the radiator stopped filling with air.

Another indication that all is not well is if the water coming out when you bleed the radiator is blackish instead of clear.

Have you ever flushed/treated the system?

Could be worth a go.

HTH Dave R

P.S. not talking about power flushing - just running with a treatment in for a week. There used to be regular threads about the benefits/not of power flushing. Basically you can save a lot of money by cleaning out your system yourself e.g. by taking individual radiators off the wall then flushing them through with a hose pipe outside. Having said all this, my neighbour had his system power flushed because radiators were not heating up, and he said there was an amazing difference.