I have a Triton T80 electric shower that is running at a very low rate of flow. I think the inlet filter needs cleaning but don't know how to get to it.

Having a shower and turned the heat setting down to cold... on the rotatory knob... there was a dull bang and water stopped coming from the hose / head but is pouring out of a safety overflow on bottom left corner. Took shower apart to see if it's anything obvious, checked flow through outlet...

Triton combi hp thermostatic mixer shower.water lukewarm at hot setting and not very good pressure.tried changing shower head no difference.any ideas?

My shower only let out cold water even when I put the temperature up, can some one help me