Expansion valve leaking

[Bodge_the_Builder]

Today I replaced an upstairs radiator with a smaller model. Old one was a decrepid - approx. 1000mm (W) x 700mm (H) and the new one 600mm(W) x 450mm (H).

All appeared to have gone OK. TRV valve on the new rad seems to work OK and no leaks in the rest of the system. However, I've just found a leak from what looks like an expansion release valve that comes from a T-joint on the outlet pipe from my hot water cyclinder. (I think it's the outward flow as it connects into the cylinder just below middle of the tank and there's another one directly below it near the bottom.)

The hot water cylinder is a an indirect type. I assume the system is gravity fed and the boiler is a Potterton Max condenser.

Can anyone help me? or even explain why this might be happening.

 

[chrishutt]

It's probably an air vent that's leaking, possibly an automatic one (AAV). You can stop the leak by closing the small plastic cap, if there is one. Otherwise you could replace the AAV (£5?).

 

[Bodge_the_Builder]

There is a small red cap on the top of the leaking "peice". I've tried to tighten with my fingers (while the system was hot) but it wouldn't move.

What do you recommend?
Waiting for the system to go cold then tighten with suitable pliers?
or just go ahead now while the system is still hot?

 

[Paul Barker]

Order a new aav. I nearly wrecked an old worcester last week refilling after a drain down because some clown had closed the aav, and the darned thing fired up with no water inside. Why should we have to open every casing seal to see if some boso has closed aav?

If it's broke fix it.