Worcester 28CDi Water cycling hot/cold. Water leak from AAV

[jasonfrog]

I have a Worcester Bosch 28CDi combi that seems to have developed a fault.

With the hot tap running (and the central heating off) the boiler will provide hot water for around 30 seconds, after which the pressure gauge needle will wobble around slightly for around 10-20 seconds, at which point the boiler stops heating and the needle settles back to 1 bar. After around another 10-20 seconds the boiler start heating again and this pattern continues until the hot tap is turned off.

The automatic air value is now also slowly leaking water, when the boiler is in use and for a short while after the boiler has been used. It stops leaking after maybe 40 minutes to an hour or so. The AAV doesn't have a cap.

Prior to this happening I had drained the central heating to replace a radiator. All the radiators were then filled and bled. However at come point in the course of doing that I managed to cause both the indicator lights to flash slowly, indicating an overheating cut out. This occurred once and did not happen again after resetting.

Any suggests on what might be wrong with it?

 

[muggles]

There's possibly still some air in the boiler, I'd be looking to replace that AAV for one that works properly

 

[jasonfrog]

Some further info about the AAV, just in case it matters. It only leaks when the boiler is in use and for a short while after the boiler has been used. It stops leaking after maybe 40 minutes to an hour or so. It's a slow leak.

Any advice on clearly air out of the boiler?

In case it is useful to anyone. Here is a link to a pdf of the service manual.
https://dl.dropbox.com/u/17574502/servicemanual.pdf