Triton shower absolutely roasting!

Hi folks, hope you can help.

We have a Triton shower in the house. After reading some information regarding which type of shower it is I'm confused. I think it's a manual mixer as it has both a hot and cold feed?

Anyway, to my problem. The shower is very hot, unbearable even, and when I try to turn the temperature down the flow slows until it just stops. I don't know if the cold water feed is working, does that make sense?

Also if I turn one of the taps on in the sink, the shower flow is affected.

Please help, thank you

sounds like you've got a blocked filter or stuck non return valve.

Cheers, thanks for the reply.

Sorry about this but where are the items you mentioned and can I fix the problem myself?

Apologies for being totally new to this!