Shower dial issue hot water

[Spider-Ali]

Hi am wondering if I can get some advice on this issue. Shower was working fine until Saturday when the dial only works when turned to cold water side and hot water side doesn't work. Other shower works fine and all taps have hot water coming out. Just wondering if get some on advice on what could be causing this.

 

[Ben-gee]

Debris in hot inlet filter, stuck non-return valve in hot inlet, faulty thermostatic cartridge, stuck non return valve in hot pipe work, someone turned off an isolation valve in hot pipework.
I’d probably check in that order - although the last one first I suppose!