thermostatic shower control

[JohnofGwent]

My thermostatic shower/mixer temperature control has gone a bit sensitive. That is to say the slightest movement of the control turns the water from very hot to freezing, and it is a bit of a fiddle to balance it. It is 2-3 years old. I have stripped it down as far as I can and found no dirt inside. Does this mean the thermostat is kaput.
Any suggestions for a fix would be welcomed.

 

[masona]

You don't say what sort of heating system you have,but if it gravity type the cold feed should come from the cold storage tank for equal pressue.If the cold feed come from the rising main then you will have difficulty getting the balance with the hot water pressure.

 

[JohnofGwent]

Thanks Masona. Cold water from cold tank then via pump along with hot. Must say all worked OK for last 2 yrs. Problem apparent for last 3 months.