Air in Vaillant 828E combi system

16 Oct 2004
Reaction score
United Kingdom
I have a Vaillant 828E Turbomax combi boiler which feeds an 8 radiator system. Every thing works ok, but I keep getting air in the system and have to bleed two rads upstairs approx, once a week. I replaced the PRV last year as the overflow pipe was dripping and that was cured. The only other problem has been the diverter valve sticking which i removed and cleaned and has worked fine since. Could air be entering at the diverter valve?

The pressure in the system doesn't seem to change (except when I bleed the air) and is between 1.0 and 1.5 bar. Any suggestions gratefully excepted.

Sponsored Links
Unless the pressure isn't high enough (unlikely), it sounds like a corrosion problem. In which case the gas is hydrogen, which you could test.

Add say Fernox Restorer, run, drain, then an inhibitor such as Fenox protector. Both these are available as syringes you can inlect into a sealed system reasonably easily.
ChrisR, if it was corrosion, wouldn't you expect the hydrogen to collect in all the rads, not just two of the top ones? And surely it wouldn't generate fast enough for them to need venting every week?
Sponsored Links
Thanks for the replies :)

The Boiler is upstairs, mounted in what appears to be the old immersion cupboard, the flue exits through the loft/pitched roof of the house.

So the bottom of the boiler is approx. the same height as the top of the upstairs rads.

How do I test for hydrogen?

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local