On Sun, 27 Nov 2011 15:18:41 -0000, Simon T wrote:

Well apparently she seemed to think the heating didn't come on at all
the other morning, so I'm thinking faulty electrical switch on the CH
actuator.

Or the mechanicals have got a bit gummed up and there is quite enough
torque to operate the switch. It could be gunk in the valve shaft to
the wet bit or the rack/pinion that drives the valve open.

--
Cheers
Dave.