Automatic air vent leaking

5 Oct 2007
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United Kingdom
My central heating system is open vented and I have an Automatic air vent leaking water when the central heating is running. The vent was replaced recently as the previous one was also leaking. The leaking stops when the central heating shuts down. The heating and hot water works fine. My boiler is an oil fired Worcester WM12/19 about 6 years old. Would any of you kind people have any idea why the automatic air vent would be leaking or was i just unlucky enough to buy a duff replacement :mad:
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I bought a Auto bleeder from B&Q once ...... That leaked too ....... I just gave up & bled the rad myself.

In my experience theys just not very good ..... Nice idea tho :eek:
they usually leak because poor water quality eats the rubber seal or deposit crap on it and prevents it closing.
My central heating system is open vented and I have an Automatic air vent leaking water when the central heating is running.

They leak, it's the nature of the beast.

They have a float-operated needle valve that seals a small orifice. A small bit of grit can partially block the float seat and heating systems are full of small bits of grit; swarf, sand in radiators, corrosion sludge, limescale, etc..

The only ones that are half reliable are the big brass Winn's/Brownall jobs. You don't see them often because they're about £90 each. Even then, there should be an isolating valve below them (to allow them to be isolated or removed for repair). The outlet should permanently piped to a drain.

Domestic ones should be left open for a week after filling the system. After that, there shouldn't be any air left in the system, so you shut the cap on the outlet.

Blasted things should be banned. And that stupid felt roll pipe insulation.
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Thanks for your reply Onetap, I was worried that I might have a problem with my system. I installed it myself about 6 years ago and i'm not a plumber or heating engineer so I thought I may have screwed up somewhere. As I said on my first post heating and hot water works fine. I must admit I couldn't understand why a new aav would leak as i've had one to bits before and from what i could see there isn't much in em to go wrong apart from any debri and gack stopping them sealing shut once the air is out. I did wonder whether water turbulence when the pump is running was shaking the float about causing the thing to leak but I wasn't really convinced about that. I reckon I might just buy a manual one from the plumbers merchant and to hell with it. :evil:
Use a 1/2 FI coupling with a 1/2 rad vent screwed in (uses standard bleed key) off pipe upstand.

The small soldered finger vents (with the knurled cap) always block up. The screwdriver ones always leak on the washer.

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