Triton t80si shower is very hot even on a low setting then fluctuates between hot & cold, pressure switch is not activating but pressure seems low any advise will be gratefully received.

If the water temp is fluctuating from very hot and cool the problem could lie with a blockage in the inlet to the shower, scale inside the heater can, shower hose needs replacing or the shower head needs to be cleaned The problem is a "slowing" of the water across the heating elements which causes the water to pick up too much heat