Constantly Bleeding Air from highest Radiator

[RK_London]

I have 3yr old unvented system with a Vaillant 637 Ecotec plus boiler. The heating system was upgraded from a vented system as a part of a house extension which included extra underfloor heating, a larger 300L cylinder and a new vertical radiator in the bathroom directly above the boiler.

When I bleed the system, the only radiator with air is the new vertical bathroom radiator above the boiler. Every few days I check the radiator and I always have air at the top. As this radiator is also the highest point in the heating system, I was thinking the gas might be hydrogen not air.

Should I drain system and add an inhibitor?

Any help would be appreciated. Thanks.

 

[Madrab]

If it's a metal bleed valve, next time you open it, good gloves on (not latex) and just open it the slightest amount till you can just hear it hissing and try and light it (stand back) if it's H then it'll flame.

 

[Johntheo5]

If you are bleeding it with the boiler/pump on then you may actually be drawing air into the rad (even with a sealed system) if no water issues after venting the air?. If no water bleeds out, stop the boiler/pump and vent/bleed again.
Also check boiler pressure with boiler shutdown and when running.

 

[RK_London]

Thank you for the replies Madrab and Johntheo5.

I always bleed with the system switched off. The bleed issue with radiator has been going on since last winter - hoping that it was air the would eventually bleed out. I have monitored the boiler pressure over the year and it looks stable- 1.1 bar when cold going up to 1.9bar at target flow temperature.

I've had a pipe banging issues since the new boiler was installed (noise every 15 minutes all day) usually around pump over-run. Installing plumber was a decent guy and came back 18 months ago to fit a bypass valve but didn't solve problem. I was hoping the radiator bleed issue was the problem.

I will try collecting the gas in a bottle before igniting - abit nervous putting a flame on the escaping gas in case it is hydrogen.