How to Replace a Boiler Auto Air Vent (UK)
Swap the AAV on Worcester, Vaillant, Baxi combis. Cures loss-of-pressure and gurgling faults.
Worcester BoschVaillantBaxiIdealWatts
Symptom
Boiler pressure drops slowly overnight with no visible leak. Rads gurgle. The AAV float sticks, either venting water or trapping air.
OEM part numbers
- Worcester Greenstar — 87161029060.
- Vaillant ecoTEC — 0020007194.
- Baxi 800 — 720012701.
Fit
Isolate flow and return, drop pressure, thread new AAV with PTFE. Open the top cap ¼-turn permanently — sealed shut AAVs don't vent.
Frequently asked questions
- Should the AAV cap be loose or tight?
- Loose by ¼-turn. Fully tight defeats the vent function.
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