Turn off boiler and let it cool right down.
Close both valves on filling loop and disconnect it.
>>Find drain point, drain enough water from system.
Replace AAV.
Fill/purge boiler.
Restart.
>>Edited to add the step previously omitted, as observed by ChrisR.
I have no reason to think that he or that he isn't, so I simply stated the facts. You're the one giving misleading information; this time it's about the legislation. What will it be next time?
If that is so then I dont think that an anonomous "Softus" should be encouraging him to do something which might place him in danger!
If you do that you're likely to spray the room.
Drain enough water out from a drain point to let the pressure drop to zero.
I wouldn't worry about it being cooled right down, or disconnect the filling loop - though it could be letting-by I suppose.
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