Automatic Air Vent leaking - Worcester Bosch Greenstar 37cdi

25 May 2003
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United Kingdom

I have discovered a slow leak on my boiler. Having taken off the front cover and had a good look I have identified the part which is leaking as the automatic air vent. Having googled the part looks like a replacement is about £10.

Have found from this forum that it is a common problem on combi boilers but couldn't find anything specific to my boiler - the Worcester 37cdi. Anyway, is this part relatively easy for a diyer to replace? Looking at its location it seems a bit tricky to reach. If I get someone in to replace it any rough ideas on what I should be paying for this type of boiler to be fixed.

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It's not too bad a job. Isolate and drain boiler as per instructions.
Release securing pin, twist and pull to release the unit. Make sure the o ring comes out with it.
Grease slightly and install new. If the pin doesn't seem to go back in properly then you haven't got it in correctly. Don't force it.

Good luck.
If there's no pin/clip then it will be a twist out type.
Unscrew anti clockwise as normal.
Well I have the part, isolated and drained the boiler and taken the old one out. But cannot get the new one in. It is a push in and twist one but the hand space around it is very limited and I am bu**ered if I can push it and twist so that the side lugs on the aav can locate properly so it locks in place

Is there something really obvious I am missing on the technique front.

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Doh - just reread your first post where you mentioned grease. Just put a bit on it and hey presto job done. thanks for all the advice.
I realise that this thread is very old, but I found it whilst searching for solutions/answers to the wonderful problem I've discovered tonight and it seems pretty much the same issue.

Tonight, as the boiler switched on to heat the hot water (Worcester Greenstar 40CDI) we heard a large bang, then another....after investigating, taking the front off the boiler, I discovered that the auto air vent had been leaking. I could see water around it and beneath it. Looks like it's been leaking for a while as there is a lot of dried water below it.

When the boiler came back on it got to around 75c, then switched off (automatically, fail-safe I guess) BUT THEN it went on to 102c !! (I watched it go to 98,99 and then it showed 00, 01 and 02- which I assumed is 102 since there are only two digits on the display)

I have this for 10 years and never saw that kind of temp before.

My question: is it likely the two are related? I think so, but I'm no plumber. The banging I assume is air getting in to the system (as well as water getting our of the system) and the air and water in central heating from my knowledge equals BANG! Would the air around the combustion chamber be a reason for the temp going off the scale?? I'm clearly guessing here.

I've sent the better half off to get a replacement bottle vent so I plan to swap that over.
Wont fix your problem of banging, probably a duff pump they tend to cut out every now and again causing overheat, hope you know how to check the boiler wont kill you when you put it back together
it was the AAV; bled the system, replaced aav - working again.

banging was air in the system. air and bangs both gone.

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