Vaillant/(Grundfos) CH pump AAV

Last week I fitted an external expansion vessel to my Vaillant CH system. While I was there, I flushed and re-inhibited the system.

Having been bitten before, I pressurised the system initially with just water - fired up - no leaks. Great.

Added flush, ran system for a couple of hours. Fine.

Drained, added inhibitor. Refilled and (you can guess this bit) the AAV on the pump started ****ing water.

A speed-Google later, I removed the valve, cleaned it, refitted, and so far (4 days in) no leak, no pressure loss.

When I located the leaking AAV, the plastic cap covering the spout was hardened and cracked off.

Now my pump (clearly labelled as a Grundfos 161015) is a Vaillant VP5/2. The AAV is a metal cap which screws onto the plastic body of the pump (as shown).

However, a search of Vaillant suppliers - including Vaillant - keeps returning something which isn't that, but a complete brass body which screws into something.

The boiler was fitted in March 2002 (!!!) and has this on the inside:

TURBOmax VUW GB 242/2-5
TURBOmax Plus 824 E

Is this a case of I need to buy the complete brass assembly, but just use the screw on cap ?

the cap is only a dust cap, I wouldnt go worrying about it just leave it as it is

Correct they are an AAV complete bottle, however you can unscrew the head off it and renew the one in situ.

Cheers guys. Managed to order the part at a ridiculously low price via eBay

https://www.ebay.co.uk/itm/Vaillant...2-838-2-E-Bottle-Air-Vent-061707/331398532481

Arrived today, so will fit it when possible.

ARGHHHHHH ...

swapped it out (fitted perfectly) and it's leaking from the threads !!!!!! The new part comes with an O ring seal .... how tight should it go ?????

E2A: OK, so removed, checked all threads were OK (they were) and replaced but was a little less cautious about tightening. Repressurised system - no leaks.

Am currently running heating, but - touch wood - all seems OK.