Thanks guys, got a local plumber out to take a look who confirmed the problem being with the motorized valve - unfortunately there was some wear/damage in the unit - fortunately replaced at a modest charge and all up and running again.
Nope, certainly not since we've been here - and as far as I know not prior to that. House was a new build some 15-6 years back and if I was a betting man I'd say it was original.
Hi, I'm hoping that you good folks may be able to give me some pointers for initial ideas on an issue that's developed today - before I go down the route of calling in the plumber, only to find out it was something I could've sorted myself. I'll openly admit to not being overly technically...