Air in Bathroom Radiator? AFter about a month....

[bob2805]

Three years ago we had the boiler changed to a worcestor 30Cdi. Condensing Boiler. We had a Magnaclean fitted the following year. At the time of fitting the new boiler we had the system flushed.
Only started to notice it this year maybe due to the demand on the heating due to the cold weather. Anyhow - I have noticed that the bathroom radiator which is about 6ft away from the boiler(boiler in cupboard) gets air in it after about a month. The top rung of the towel radiator goes significantly colder than the other rungs. When bled the air comes out and the system then requires topping up. This lasts for about a month and hence it requires it again. I have done this a couple of times now and think there may be a problem?
I have no idea how long it has done this for prior of whether this problem has been longstanding?
The boiler is due for a service soon so was going to mention it then....can anyone help with what it might be?
We have 8 radiators in total on the system 2 of which are large vertical radiators downstairs. There are no problems with any of the other radiators - they get warm all over and when these were added about 8 months ago the system was treated with some Fernox Inhibitor.
I have no idea what is causing this?
If you need any more info just ask....I would love to get this sorted!

 

[WabbitPoo]

well when we had that problem, it was caused by a leaking joint.

 

[John506]

Indeed you can have an opening that is too small to let water out, but will let air in, know as a micro-leak.

 

[bob2805]

Ok so say I have a microleak is there a way I can diagnose it?

The pipwork to the radiator that gets air in is behind the wall and all soldered. I think it tees off the main run and is the first on the system?

Most of the radiators are switched on to max so could I turn off the valves to this rad and see if the actual rad is drawing air in(its a towel radiator)?If these valves are turned off then if it isn't air being pulled in at the rad does this mean the pipes maybe at fault and will air then gather elsewhere in the system with the valves closed to the towel radiator(highest rad on the system)

Would like to try and diagnose to some degree before I get someone out.

Could the boiler be at fault in any way?

 

[WabbitPoo]

The leak, if that is the problem, could be anywhere. We had two in the loft (when our boiler was changed to a higher pressure combi system) and one under the units in the kitchen (plumber bodge originally). However in both cases, we had water dripping out, so easier to find! Have you spotted any evidence of water anywhere it shouldn't be?

In both cases, air wa eventually finding its way to the high point of our CH system, namely the towel rail, so don't assume that the rad with the air in it is the problem itself.

 

[joe-90]

Indeed you can have an opening that is too small to let water out, but will let air in, know as a micro-leak.

How does that happen if there is a permanent positive pressure?

 

[bob2805]

Not spotted any signs of water leaking out....most of pipes contained.

This is going to be difficult to find if it depends on observation alone.

What I don't get is the fact the leak could be elsewhere on the system and still working its way to the top radiator....well I do but don't because if it were say mid system between say I don't know 4th and 5th radiator in the house the air would travel along and settle in the next radiator and that would be the radiator to bleed instead of the bathroom one(1st on the system?).

How the the hell do I find it if logic like that doesn't work?

 

[bob2805]

Indeed you can have an opening that is too small to let water out, but will let air in, know as a micro-leak.

How does that happen if there is a permanent positive pressure?

What do you mean by this? I don't understand?

 

[joe-90]

You can't get something in when there is a constant pressure from something trying to get out. If you drill a hole in a pipe water will come out - not air get in. Everything in science goes from high pressure to low - not the other way round.

 

[45yearsagasman]

Don't assume that it is air.It may well be hydrogen bubbles forming and depressing the water level in the rad.You can test for hydrogen by holding an inverted container over the rad vent and if it's hydrogen it will collect in the container and can be ignited.
If this tests positive then it's an inhibitor problem.

 

[bob2805]

Thanks, I take it I can do this when I next bleed the towel radiator with the bottle over the top as you described?

 

[45yearsagasman]

Yes, wait until you need to bleed rad and do the inverted container test and that will prove hydrogen or not.I use any wide contaner,a bottle may no be suitable.Any gas collected will "PoP"

 

[bob2805]

Not spotted any signs of water leaking out....most of pipes contained.

This is going to be difficult to find if it depends on observation alone.

What I don't get is the fact the leak could be elsewhere on the system and still working its way to the top radiator....well I do but don't because if it were say mid system between say I don't know 4th and 5th radiator in the house the air would travel along and settle in the next radiator and that would be the radiator to bleed instead of the bathroom one(1st on the system?).

How the the hell do I find it if logic like that doesn't work?

Anyone answer this?

 

[joe-90]

Little air bubbles will travel in the water flow circulated by the pump. When you switch off they migrate to wherever physics says they should.