Air in ONE radiator

In_for_a_penny

Hi,

For some odd reason, I seem to be having to bleed one particular radiator as it gets air in, probably once a week. It's not a great deal of air but nonetheless it keeps recurring. The central heating is on every day and appears to be working as it should and I cannot find any leaks. Does anyone have any ideas why this keeps happening? One suggestion is that air may be entering back in through the expansion pipe (in the tank) in the loft. The system contains anti-corrosion fluid. The only other thing I've thought is that I did replace this radiator earlier in the year and the system may still have a small amount of air in and keeps finding its way to the uppermost radiator but I thought would have gone by now!

Thanks.

:mad:

silvercar

I've got the same problem so I am hoping sone one can help.

david29dpo

Check to see there is water in the header tank and the ball valve is working.

mikey72

Is there any sign of white on the valve, or pipework going into the radiator?
Possible small leak, sucking air in, rather than leaking water out.

silvercar

could be a chemical reaction with the anti-corrosion fluid:

anti-corrosion stuff + sludge/ scale ----> dissolved sludge + gas.

So the gas ends up at the tope of the highest point radiator and you bleed it out.

agent_orange_2

There's always the self-bleeding valve. http://www.langdoneuropean.com/durovent.htm

Wookey

In_for_a_penny wrote: »

Hi,

For some odd reason, I seem to be having to bleed one particular radiator as it gets air in, probably once a week. It's not a great deal of air but nonetheless it keeps recurring. The central heating is on every day and appears to be working as it should and I cannot find any leaks. Does anyone have any ideas why this keeps happening? One suggestion is that air may be entering back in through the expansion pipe (in the tank) in the loft. The system contains anti-corrosion fluid. The only other thing I've thought is that I did replace this radiator earlier in the year and the system may still have a small amount of air in and keeps finding its way to the uppermost radiator but I thought would have gone by now!

Thanks.

:mad:

Is your boiler inside the house or outside in a boiler house/shed etc?
If you are on a pressurized system, are there any blow of valves or tundish's showing on the pipework?
The vent in your roofspace is it for hot water or does it vent for heating?
The air that you are venting from the rad, is it flammable? (hold a lighter or match to it when you open the rad's air vent, if it burns its gas and is a sign of corrosion, if it wont burn its air).

In_for_a_penny

Firstly, thanks to all those that have replied.

david29dpo:- Yes, there's water in the header tank and the ball valve seem to be working as it should.

mikey72:- I cannot see any evidence of 'white' deposit on valve or radiator pipework.

silvercar:- The chemical reaction theory sounds plausible. Thinking back, it seems to have begun sometime after anti-corrosion or rust inhibitor was added - but could just be coincidence I suppose.

agent-orange:- Good idea re self-bleeding valve. Hadn't thought of that.

wookey:- Boiler is indoors (well in garage). It's not a Combi so wouldn't have thought pressure would be an issue. The vent in the loft is from the copper water cylinder so presumably heating & hot water? Haven't tried the flammability test. (I probably wouldn't have enough time to strike a match before water appeared from bleed valve anyway).


One thing that has occurred to me is that the expansion pipe into the header tank doesn't actually 'sit' in the water in the header tank. It is just bent over the side (above the water level). (If that makes sense). So I'm wondering if, because the pipe end is not actually in the water in the tank, it's drawing air back in through that way?!?!?

foreversummer

I cannot be any help whatsover i'm afraid, but I do have the same problem with one of my radiators, a towel radiator in my bathroom. Several plumbers have had a look and none can see a problem. I even had some pipes re-routed as one thought this would help. Still I have air.

Foreversummer

Wookey

The vent over the header tank doesn't need to be piped into the water, if the system is properly piped/setup then air shouldn't enter in thru the vent. Is there pipework hidden/buried between the boilerand the house? and is the rad that needs bleeding located near the boiler?

keystone

In For A Penny

Under no circumstances should the vent pipe be under water. The system you have is called "open vent" and its designed to be that way. The vent is there to allow expansion of the water in the system when it heats up. It will have been designed so that air is NOT drawn down through the vent unless something has gone wrong.

Many older systems suffer from air in one radiator - its normally the highest on the system. If the boiler is old and the heat exchanger gets scaled up then sometimes what is called "kettling" occurs when air is released from the water.

Sometimes you get hydrogen released as a result of the corrosion whoch will occur. One poster suggested that you use a match when bleeding the rad - that will tell you if you have hydrogen or air but as you say there isn't enough gas released before the water comes out then what you are getting is minimal and I would suggest your "problem" is quite normal.

Your plumber should be able to advise you on the courses of action if he feels they are necessary but PLEASE do not even think about extending either of the vent pipes so that they are submerged.

Cheers