Accessing a Crosswater Thermostatic Valve on a Metro Bathstore Valve

[alexuk]

[I posted this morning but I was unregistered - here it is again]

My shower bath has an old model of the 3 valve Bathstore thermo valve (Can't post more than one link as a new user).

The thermostatic valve is seizing up, so I thought I'd take a look inside. I removed the handle and the first collar and I can see the end part of the cartdridge. If I look at this (not the same model but similar)
https://www.youtube.com/watch?v=2pVuvG6q84A

it looks as if I ought to remove the 3rd collar too. However if I just try to unscrew it by hand it won't come off. Do I need to remove the plate first? If so, the plate actually has two caps next to the temperature control. Are there two screws under them? I tried to use a Stanley knife but I can't get them off. If I can get away without removing the plate, I'd rather do that so that I do not have to do the silicone around again.

Thanks for any help. Once the collar is undone I am hoping to access the cartdridge relatively easily. I think it is a Crosswater one.

Here's a picture.

 

[Riley]

Best bet is to contact bath store in the first instance and see if parts are even still available. Might save you dismantling for no reason. You may breath a little life back into the shower by descaling the thermostatic valve. My bet would be that parts won't be available so you'd possibly be best off looking at a new shower in the long term. Try also shower dr