UK trade guideBoiler Spares 5 min readUpdated 11 July 2026

How to Replace the Auto Air Vent on a ATAG i36 Combi (UK)

Step-by-step UK guide to replacing the brass automatic air vent on a ATAG i36 Combi. Part numbers, torques, commissioning.

ATAG

The part

Fit a new AAV on ATAG i36 Combi when the boiler airlocks on start-up or the pump makes gurgling noises after refilling.

Isolate safely

Isolate flow and return, unscrew the AAV from the top of the pump head or air separator on ATAG i36 Combi.

Fit and commission

Loosen the AAV cap one full turn once refitted — a fully-closed cap defeats the float.

Recommission checklist

Refill the ATAG i36 Combi to 1.2 bar cold. Bleed high-point radiators and the internal AAV.

Run a full flue-gas analysis after 15 minutes. Log the reading against the OEM commissioning envelope in the Benchmark book.

Frequently asked questions

Any special height?
Fit the highest point of the ATAG i36 Combi circuit — that is where entrained air collects.
How often should I service?
Annually — the float sticks with sludge in unfiltered systems.
Do I need to notify the manufacturer?
Only if the ATAG i36 Combi is in warranty — ATAG require log of any part swap for labour claims.
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