You will need to strip it out and place it in a bucket of descaler, or replace the thermostatic cartridge
Yes I figured that but how do I strip it out? There's a grommet on the top of handle - is there a screw inside to free off the handle, please?
Do you have the model name?
If it is a bar type then there is a screw under the coloured cap
Remove the screw and pull off the lever
Undo the nut that holds the thermostat in place
No it's not a bar type - it is a single round valve with built-in lever on the front
There's a 25mm diameter screw vaklve on the top with a flat blade style groove on it. Undo that?
See if you can identify it here?
Yep it's the first one that appears on the main spread on the page
Can you tell me the name?
I went on the link you provided me earlier and the main display picture is the very shower mixer I have. A name is XXXXX XXXXX It is the simple barrel with narrow vertical lever. I have removed the top screw-in piece and filled the inside with Viakal to see if that eases it.
The big picture at the top?
Looks like the Sonique further down the page?
Maintenance on page 23
Yes Sonique, that's it.
The instructions (save a copy) tell you how to clean it and look after it, if that does not work then you can order spares direct from them and replace the cartridge