Help - Water leaking from Automatic Air vent on boiler

[NeilPalfreyman]

I did some work on my heating system today, which is a pressurised system with a Worcester 35CDi II combi boiler.

I drained it, replaced a couple of old radiators and re-filled it. All went well, no leaks on repressurising, but when I fired up the hot water it vented steam and hot water out of the "automatic air vent" on top of the boiler for about a minute, which I assume was clearing air trapped in the heat exchanger?

The venting stopped and the hot water works fine but I'm getting a substantial continuous leak out of the vent now.

There's a small black plastic cap on top of the vent (like a car dust cap) and if i tighten this up the flow stops but I'm worried that this is just closing the vent and that it should be left open?

What I think may have happened is that the venting (which was quite forceful) has pushed a load of crap into the valve which is now stuck open.

Any ideas? Can I just tighten that cap or should I leave it off and get someone out to replace the valve (that job's beyond me, I think!)

 

[twgas]

Get the vent replaced, if its left tightened for a prolonged period it might cause damage should air collect in the h/ex.

 

[NeilPalfreyman]

Get the vent replaced, if its left tightened for a prolonged period it might cause damage should air collect in the h/ex.

Cheers, Mick - that's what I thought.

...been looking at the manual and considering giving it a go myself - do you reckon it's DIYable?

Looks pretty straightforward but then these things always do, don't they?

 

[Dan Robinson]

It is straight forward, but required the opening of the combustion chamber so you need a gas engineer to do it.

I dare say the boiler is in need of a service anyway.

 

[NeilPalfreyman]

Got a bit of a post-script to this post.

I had the system drained again today for some more work and on re-filling I left the cap on the offending auto air vent tightly closed until the whole system was re-pressurised then opened it (before using the boiler) to vent the heat exchanger.

As you would expect a lot of air came out but this also seems to have the side effect of clearing the blockage. It's stopped leaking water.

Is this feasible? Should I still get it changed?

 

[Agile]

I think you have correctly guessed whats happened and my view is you don't need to have it changed.

But if Dan is right about where the AAV is located you have opened the combustion chamber which we don't advise DIYers to do.

Tony

 

[NeilPalfreyman]

you have opened the combustion chamber which we don't advise DIYers to do.

Tony

Fear not, Tony - the inner sanctum of the combustion chamber remains intact

...the cap I'm referring to is on the outer case.

 

[Agile]

I still fear !

The outer case is the seal to produce the room sealed condition.

Tony

 

[NeilPalfreyman]

...the outer casing isn't sealing anything.

 

[twgas]

Am I right in thinking the autoairvent on you boiler actually protrudes through the top of the casing? If so changing it would mean disturbing the seals but opening and closing the top cap would not.

 

[NeilPalfreyman]

Am I right in thinking the autoairvent on you boiler actually protrudes through the top of the casing? If so changing it would mean disturbing the seals but opening and closing the top cap would not.

exactly.