The temperature control has become very stiff. It appears that the themostatic control valve is the problem. I have opened it all up and found the cartridge, which appears to be an SA30039, like this http://www.ergonomicdesigns.co.uk/SA30049-Hudson_Reed_Replacement_Thermostatic_Cartridge.html
A local plumbing shop I tried suggested removing it and soaking in Soda Crystals (presumablt to try to reduce limescale build up) That helped a little, but not much
So my next stage is to consider an active acid based descaler. Is this a good idea? Or is it posble to dimantle it further and manual clean it?
Or does anyone have any better advice? The valve itself still works, but as it stands I am the only one in the house strong enough to turn it.