Main ECO 30 Auto Vent Valve

[rizla01]

Hi all.
The vent valve on top of my 9 yr old Main 30 ECO combi is pretty cruddy and lets only a tiny amount of water past the plastic screw at top - no air at all.

I needed to re-pressurise my system 4 times yesterday and i have noticed considerable dripping from outside plastic pipe.
Is the AVV likely to be the culprit or does it sound more like the expansion tank?
How do I test to find out?

Thanks

 

[Madrab]

The plastic pipe outside should be the condensate so that's normal
Any water from the AAV means that the valve is passing and needs replaced, if it is passing water constantly then that can drop the system pressure. You should have a copper pipe outside too, the pressure relief pipe, check that isn't dripping
If the system pressure is close to 3 bar on the boiler gauge then the expansion vessel EV needs tested. You'll need an engineer in though as the EV is within the sealed chamber and is not a user accessible location.