Air in Sealed Central Heating System Advice

[wedge69]

Hi,

We have a radiator at the top of our stairs on the landing that seems to accumulate air. Usual symptoms of being slightly cold on the top but roasting hot at the bottom. All other radiators are ok.

I'm confused as to where this air is coming from as I am not noticing any visable drop in pressure in the system, it just fluctuates between 0.9 and 1.2 bar depending on whether the heating is on or not. There's also no visible sign of obvious leakage either.

What confused me more is that I just bled the radiator and air came out for maybe two seconds, but the system pressure dropped from 0.9 bar to 0.5 bar, which sounds like a lot to me, but maybe that is normal? I topped the system back up.

May be worth adding that this is a new build house and only the second winter of having the heating on, so could it just be the air that was in the system when it was originally commissioned just working its way out?

Any comments welcome as to whether this is a problem or just one of those things.

 

[dcawkwell]

Try lighting the "air" that comes out.
If it goes with a pop you have an electrical fault and the "air" is hydrogen
cause by electrolysis of the water.

It is also possible that if you have all thermostatic valves on the radiators that the pump is cavitating if all the thermostatic radiator valve shutdown or there is restriction in the piping.

 

[wedge69]

Thanks. No TRV on this radiator, the others in the house do.

What kind of electrical fault can you get in a central heating system?

 

[dcawkwell]

Thanks. No TRV on this radiator, the others in the house do.

What kind of electrical fault can you get in a central heating system?

Small current passing through the water will split water.
Try and light the gas from the radiator will confirm.
Can be caused by poor earthing or a wiring fault somewhere.

 

[wedge69]

Thanks,

Our system is plumbed with plastic pipes, could this still be the case? Would that explain why there appeared to be no pressure drop even though air was getting in the system?

 

[dcawkwell]

Thanks,

Our system is plumbed with plastic pipes, could this still be the case? Would that explain why there appeared to be no pressure drop even though air was getting in the system?

Although I think it unlikely it is possible they used non barrier pipe on the central heating system. This will allow air into the system.
Check some of the piping for the central heating is should say BARRIER along it. If not your system will be rusting.

 

[wedge69]

Can't really see much exposed pipe work, so can't check that. I would assume it was the right stuff as all the other people on the estate would probably have tge same problem!

I appreciate all your thoughts though.

Out of interest, what should the drop in pressure be between a hot system and a cold one, or does it depend on the size of the system?

 

[gigz]

If you haven't really used the heating, and only topped it up a couple of times i wouldn't worry about it. Air finds its way to the top and water takes the easiest path. Make sure there's inhibitor in the system and get into the habit of putting the heating on every month at least, don't have to leave it on for ages just enough to circulate the water and give the pump a workout, also slows down dirt build up.