In article ,
"Kevin Rayner" writes:
How can I tell whether the motorised valve on the hot water circuit is
working correctly. I have been having a few problems with cold water and
noticed that the manual/auto lever on the valve has no action. Operating the
lever on the central heating valve has some resistance and is working. The
lever on the HW valve has no resistance what so ever.
Do I need to replace the whole valve?

I would expect that if the valve is open to heat the hot water.
If you switch the hot water off, the valve should close.
If it doesn't, try switching off the whole heating system which
should surely remove power from the motorised valve.
If that doesn't help, sounds like the valve is mechanically stuck.

--
Andrew Gabriel