Vaillant AAV Q.

Having worked out what the part does, and how it works, I've given it a damn good clean (both ways) refitted, and it's sealing OK now.

System pressurised, and cycled a couple of times.

Is this AAV something which works every single day, or is it's moment of glory when the system is drained/refilled ?

With the pressure off (groan) I can research a bit more.

AIUI, you have the AAV open (loosen the screw cap on the top) when you fill the system, and maybe for a few days after to let the system settle, but you don't leave the valve open permanently. If you do, weeping around the needle valve results in salts crystallising out and the valve eventually failing to close properly, so the weeping increases and eventually becomes a significant leak.

Our Vaillant boiler was almost written off by precisely this. Water dribbled down into the electrics (twice) and really f*cked it up.

We paid for a "replace everything except the heat exchanger" repair service and apart from the case and the heat exchanger, everything had to be replaced. Great value service from Vaillant.

I now have a stop c*ck between the boiler and the AAV. Don't trust the bastarding things at all now.

Tim

I'm struggling to understand this. The AAV I am referring to seems integral to the (Grundfos) pump assembly

Ah, the plastic cap (similar to a car tyre valve cap ???) seemed to have deteroriorated, and cracked off.

Does it do more than just keep dust off ???

Mine was mounted immediately above the boiler (and not by the pump). Wasn?t an integral device.

Tim

Seals it shut in the ones I know. If you leave it open, the valve will start leaking as another poster said, because it needs to stay wet to seal, and crystals will form where the seal is exposed to air and dries out.

Oh yes. It seals the AAV after you've vented the air, and stops it weeping. If yours has broken, you need a replacement.

The fact it was so deteriorated (I guess 15 years is a good life) suggests it might have been part of the problem.

Nowhere (and no one) I sought advice on this job even once suggested that after draining,flushing and refilling they system, there could be an issue with the AAV.