Attic radiators constantly need bleeding

[oscarthecat91]

I have a combi boiler heating system, the boiler is a Worcester and was installed in the past couple of years. The two radiators in the attic collect air and frequently need bleeding due to cold spots (they need bleeding every 3-4 weeks).

The boiler is in the basement and has an additional external red expansion vessel fitted. Pressure when cold is about 1.2-1.3 bar.

Any ideas how to fix this problem? It is only the attic radiators that are affected, the ones on the first floor and ground floor are fine.

 

[Iamchamps]

I would assume as the attic is the highest point that is where the air is collecting and being bled from, I would not rule out the problem being somewhere else.

 

[oscarthecat91]

I would assume as the attic is the highest point that is where the air is collecting and being bled from, I would not rule out the problem being somewhere else.

Any tips on what to look for? There are no obvious leaks as far as I can see. The heating system has recently had inhibitor added. Around 25% of the rads are brand new, the remainder from the early 90s (I am upgrading as I renovate each room). Boiler is not losing pressure.

 

[flameport]

The two radiators in the attic collect air

Does the 'air' in the radiators burn when a flame is applied to it?

 

[Madrab]

Careful when trying this, do it gently but quickly as it can melt the plastic bleed valve in no time.

 

[oscarthecat91]

I bled the radiators this morning, as usual attic ones filled with air but it did not burn noticably when a lighter was applied to it.

I have taken the tops of the TRV's off on the older radiators (dating from early-mid 90s) and I have noticed some oxidisation - could this be part of the problem? I have checked all visible pipework (in the cellar mainly, the rest is hidden under the floor) and no signs of leaks.

In addition the attic radiator make a 'ticking' noise when heating up and cooling down - they are the only rads in the house to do this.

Any further ideas? This frequent bleeding is driving me crazy!

 

[Bankrupt]

The ticking noise is highly likely to just be expansion and contraction of the radiators and may be related to the way that they are mounted and what they are mounted to. Are you sure that what you are bleeding is air and not hydrogen as others have suggested ? Is the water in your system dosed with inhibitor ?

 

[oscarthecat91]

I'm pretty sure it's not hydrogen, it doesn't readily ignite.

The system had inhibitor topped up in September 2020. The previous owners of the property had not maintained the system at all, however it was power flushed and inhibitor added when the new boiler went in last year.

 

[JohnD]

I'm pretty sure it's not hydrogen, it doesn't readily ignite.

"readily?"

 

[oscarthecat91]

"readily?"

I should have said it doesn't ignite! Really don't think it's hydrogen