Shower cartridge or total shower replacement

[Theremustbemoretome]

We bought a house which needs a lot of work and one thing is the shower - the temperature has gradually reduced down to lukewarm only on the highest setting. The plumber said if we can find out the brand then the shower cartridge (assume it regulates the temperature) can just be replaced, but if we can’t then the only solution is a total shower replacement.

If he has to do a total replacement then he said he’ll have to rip out half the wall (not sure if that was a flippant comment or not ) - is that correct, because obviously it’s tiled and these will be badly damaged? Pipes are all there obviously. Anyone know how we could possibly find out the brand? There is nothing obvious on the outer unit, but I don’t know if you can just unscrew the front and there might be an imprint somewhere underneath?

The bathroom needs replacing but we can’t do this just yet.

I'd say post the pics in some plumbers' forums. There's a good one at Screwfix
community.screwfix.com/forums/plumbers-talk.2008/

There are plumbing suppliers that can usually identify the cartridge from a photo of the cartridge. I think it's a bit hit and miss and obviously the shower will be out of action for a while.
Replacing it will likely damage the wall. It will probably require moving pipes at a minimum. When we replaced a shower valve behind a wall a section of the wall had to be replaced. We were able to get matching tiles and the mirrored tiles in your picture look like they should be replaceable, but obviously that's all extra work and cost.

Try www.showerdoc.com/shower-accessories/cartridges

or maybe

www.bathroomspareparts.co.uk/12-24-spline-12056-c.asp

There are a good number of websites that stock a large number of these. However, to identify what you need you'll need to remove the one you have and take measurements. That's the first job.

Personally, I'd take all the measurements and then email the company for advice.