Anti Vac Valve

[adjiland]

After replacing a anti vac valve should there be any noise or fissing at all once the valve cuts off or what is the norm for this, there seems to be a little fissing noise going on just wondering if that was normal.

[Bames]

There should be absolutely no hiss or fizzing from the anti vac valve. If there still is anything like that, you need to re-replace

[artman]

Once they pop shot when the boiler reaches pressure they make no noise (perhaps a bit of water droplets boiling off for a few seconds).

Maybe there is a bit of crud caught in the seal or the seal between the valve/boiler is leaking. If you can fire up machine while looking at the valve it should be obvious where it's coming from. Beware live power etc etc.

Cheers