Installing automatic bypass

If you can be bothered then do it all 22mm then. The bore of the valve is probably not much more than 15mm anyway in reality.
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Job done = no more overrun noise :)

Thanks guys.

Drained from the boiler as suggested into a new/clean bucket which I then popped back in the expansion tank so as not to lose any inhibitor.

I've set the bypass to 0.2 bar. Tried dialling it up while feeling for the pipe to warm up but then the CH turned off (forgot to set stat higher) and of course the bypass kicked in and got hot whatever the setting was at the time!

I gather 0.2 bar is "typical"? Do I need to be any more scientific with it?


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