'98 Rover 216Sei but probably not model specific
Thought it might save someone a problem in the future to post my
Cold / Hot knob has always seemed springy in action and suddenly
became very difficult to move.
Stripped out heater controls and found WCV operating wire kinked and
therefore not operating the valve at all.
The valve itself was found to be very stiff but freed up quickly with
a squirt of Plusgas and is now well greased both to lubricate and
provide a bit of future protection.
Cold / Hot now working better than ever and therefore it might be
worth paying the valve a bit of attention when doing a service.