Turbmax Plus 824 question

[weslp00]

Guys,
Can anyone help me with a problem with regards the heating side of this boiler?
Getting air in the highest rad. Everytime I bleed the air comes back gradually but it is very gradual. Been going on for the last few Winters and now its noticeable but still slowly building up in the one rad.
Pressure doesnt drop on the gauge and from cold the gauge says 1 bar and will rise with a boiler temp of 74 dgrees to 2 bar. But when cool goes back to the same pressure when cold. The only time it drops pressure is when I bleed the air from the rad.
Boiler is about 12 years old and not been serviced for a while.
I suspected the expansion vessel which I dont think has been recharged. There is no water coming out of the overflow.
Cant see any leaks unless it is under the downstairs floor. But then how does air get into a pressurised sytem and what is happening to the water I am topping it up with.
The radiators are much older than the boiler fitted in '92 but have been flushed and the coolant ran clear so they are in good shape.
Any ideas please???

 

[flameport]

Are you sure it's air?
Next time, hold a flame next to the bleed valve and see if the 'air' burns.
If it does, it's gas caused by the radiators corroding.

 

[weslp00]

Hi flameport,
Thanks for the reply! I forgot to mention that I tried this one a few times when bleeding the rad with the air in it and it didnt light up or burn even when I slowed the bleed down so it didnt blow the match out !
Also been running inhibitor and tried a leak stopper for this season!
Any ideas its driving e nuts!