Air build up in towel rail rad

[rosstheboss]

Hi
I'm looking for some help in resolving an issue with my bathroom towel rail radiator filing with air.

This radiator has always had issues with air, I have had a heating engineer take a look at it, he tightened up the connections and added that sealant chemical to the system (I forget what it's called but it is supposed to seal leaks from the inside of the system, it's an additive). This didn't help at all and before long the rad was gathering air inside again.
A few months ago I had the boiler replaced and the problem is still present.
The pressure gauge on the boiler has not dropped yet the top 3 rungs of the rail are now full of air.
This is in a single level flat, the boiler is the highest point in the system and the towel rail being vertical is the second highest point. None of the other radiators have any problems and I don't hear any air being pumped around the system.

Any help would be very much appreciated.
Thanks

 

[Lower]

Does the air that comes out of the radiator burn? Hold a match to it when you're bleeding the rad.

If it does, its hydrogen and a by-product of corrosion that's happening inside the radiators and probably accumulating in the towel rad because its the highest point in the system.

Is it a sealed system with an expansion vessel or is there a header tank in the loft?

 

[rosstheboss]

Thanks for your reply.
No- the air coming out of the bleed valve does not burn.
It's a sealed system and I assume that the combi boiler contains an expansion vessel.