Power shower with hardly any pressure

[MustangLady]

When we had our bathroom re-decorated, we had our bath removed and installed a power shower (Triton T80i) just over 1 year now. But there doesn't seem to be must water pressure from the power shower, as we turn the heat up on the water the pressure goes down. The cooler the water it goes up again but still not to the extent we expected for a power shower. It seems to be getting worse still lately which is causing concern. Any ideas or suggestions please?

[clever trev]

Are you sure this is a power shower?? because my experence of a Triton T 80i is just a normal run of the mill electric shower, i may be wrong???