Shower water cold

[mahomedshah5]

Hi,
Shower off position used to be 10 o clock down; this has now changed to 12 o clock down. Also water is cold although water in the tank and through the taps it’s hot.
Any help will be much appreciated.
Also, how much should I expect to pay?
Thank you.

 

[Spectric]

Make and model of shower valve would help. Sounds like the cartridge has failed but more info .