Replace leaking automatic air vent

[Dry tank]

I've got a 16 year old house with an open vented system and two zone valves (HW and CH).
It all works fine except the AAV in the airing cupboard is leaking water. I've put a ball of PTFE in the cap and that's blocked it for now - and perhaps will be ok till the boiler needs replacing or it's next drained down.

Seeing as so many AAVs leak, I might replace it with a manual bleed valve. Currently, there is a soldered coupling with the AAV screwed in. I want to screw a service valve there instead with the new vent / bleed valve on top.

First question ... is it so that the high point bleed valve is really only useful when refilling the system ?

The second and last question is ... can people suggest the best combination of components to use ie service valve and bleed valve / vent so it isn't unnecessarily tall ... ? (I'm not sure a radiator bleed valve would be ideal, but if anyone else knows better, I'd be interested to hear.)

I look forward to all suggestions ...

 

[Gasguru]

Yes it's to bleed air from the cylinder coil when filling and bleed any subsequent air (and also to assist when draining down).
What thread is on the AAV?, perhaps you could just screw in a 1/2 radiator vent...no need for any valve.
If you bleed the system and bung it (do a search) you won't need to drain the system to replace it.
Most AAVs always leak or block....

 

[Dry tank]

Thank you Gasguru.
I'll probably try the bungs if it starts leaking again. The radiator vent would probably fit, but I was hoping for something to make it easier to catch water if there is any (the zone valves, pump and junction box are below the vent, so I'm keen to keep it under control). I suppose I could put the radiator vent in an elbow to make the water easier to catch ...