Huge amount of air getting in to central heating system


Postby slabber » Sun Dec 02, 2007 6:16 pm

Hi Folks

I’d be grateful for any ideas about the following problem:

A few weeks ago we were woken by extremely loud gurgling / gushing noises from the central heating pipes in our airing cupboard, which I presumed to be large amounts of air in the system. The system has never been particularly quiet (I’ve noticed odd noises before but haven’t paid any attention to them), but this was something else altogether.

Our house is only 18 months old, so I phoned the (very helpful and understanding) plumber that installed the system, who advised bleeding the radiators (heating turned off of course) and topping the system up from the mains water feed. A huge amount of air came out (one radiator took several minutes to bleed), and the system pressure dropped quite a bit. I topped up to about 1.5 bar from the mains feed.

All was well for a few weeks until this weekend when the problem has started again! Not sure about the technical terms for my system, however there is an oil powered boiler, next to which is a football-sized red (pressure?) tank. The boiler heats an upstairs radiator circuit (some radiators are set to quite low since they are in spare bedrooms), an upstairs towel rail circuit, a hot water circuit (ie through an immersion heater) and a downstairs under floor heating system. All these systems can be controlled separately. There look to be two Grundfos pumps – one for the radiators and hot water and one for the under floor heating.

The gurgling / gushing noises problem seems to start when the under floor heating system calls for heat when the other circuits are off. I have temporarily fixed the problem by manually turning on the radiator circuit and turning all the radiators fully on. The air then made its way to one of the far radiators which I bled off. I haven’t added any more mains water since the pressure is still about 1.5 bar.

From a non-expert perspective it would appear that air is entering the system from somewhere, however the plumber made the comment that for this to happen there would have to be water leaking out. I’m pretty sure this isn’t the case as I’m sure we would have seen the water. Could one of the Grundfos pumps be leaking air? Any other ideas? I’m planning to contact the plumber again, however it would be good to know in advance possible causes of this problem. I’d be grateful for any help anyone can give me with this!

Thanks - Graham
slabber
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