Thanks for the replies. Haven't had a chance to reply until now.
The show unit that is faulty is above the tap, about 75cm away.
From another thread posted, I was told it was a 'Trevi Therm Mk2'.
To fix, I would need to buy a cartridge that cost £100+.
Biggest problem: everything is fitted into the wall behind the tiles.
I had a build look at the problem. He said replacing the cartridge didn't make sense, since sooner or later something else would go wrong.
I should bit the bullet and get a new shower unit - the total cost would be just more than fitting the cartridge.
Getting the valve I gave a pic above - this was meant to be a temporary solution.
I can't find the item in screwfix.
I thought I'd ask you guys. The bathroom tap looks like a very big aerator, so wasn't sure if the valve would fit or not.
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