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Andrew Gabriel

In article . com,
writes:
I have a combi boiler with a check valve on the return side of the
filling hose. Can anyone tell me what the nut on the side of the check
valve is for? Would it leak if not screwed down tight?

It's a double check valve. The nut gives access to the bit
between the check valves. I suspect it's so you can test
they are both working. It's probably a regulatory thing,
as all double check valves have them.

--
Andrew Gabriel