Condensing Boiler - switching off

[Chuck]

It can take 15 - 20mins if there is no or little air left in the top.
You are allowed to change wrists

If you don't have strong fingers and thick skin it can help to wear a glove for holding the valve open. It's got a fairly strong spring.

If you hate waste as much as me, do it just before someone wants a bath so you can save and use some of the run-off hot water instead of putting it straight down the drain.

 

[Best]

Just go ahead turn the incoming mains water off, open a lower hot tap wait until the water stops then open the T&P hold it open until the water stops coming out the tap/T&P or (air going in) , It can take 15 - 20mins if there is no or little air left in the top.
You are allowed to change wrists

Sorry, I must have missed your above post and also posted saying same about opening the T&P valve.