I want to install a direct un-vented hot water cylinder in a flat. The install
instructions call for 22mm diameter water supply line, the main riser supply
to the building is 22m and then reduces to 15mm before the stop valve. Do i
need to isolate the main riser into the building in order to replace the 15mm
stop valve with 22mm or can I step up the pipe diameter back to 22m after
the 15mm stop valve without affecting the performance of the cylinder.

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