Bathstore thermostatic deck mounted bath and shower valves

We had a new bathroom fitted in May with the above taps. They are not attached to the shower by a pipe. One operates bath and shower the other temperature. They were quite stiff when they were first put in and got worse so the Bathstore ordered more. The second pair were installed and they got gradually worse until you could barely turn the bath/shower one on or off. The Bathstore ordered a full new unit and the plumber came again and installed them, slightly raising them to give more grip. They felt easy to turn and even my daughter could turn them.A month has passed and they gradually have got worse and now are as bad as the first and second time. It is now December, 7 months since having bathroom fitted. I am at a loss as to what to do other than have all the tiles ripped off and new regular shower fitted with normal taps. Does anyone know why this is happening? The Bathstore say they have had no other problems with these valves taps or at any other stores they know about. They have made every effort to resolve this and so has the plumber who is reputable. Each suspect the other at fault! Please shed some light!

A meeting at Bathstore with the plumber would be the best way to start.

I seriously doubt it's the plumbers fault but then again I've fitted loads of Bathstore products without issue.

Interesting one, not fitted this particular type before myself, so no direct experience.

Do you have a particular issue with limescale?

Do the heads actually touch and rub on the base of the controls? This is the only time I have had this issue with taps.

Difficult to comment really without seeing them in action.