Shower getting cold

Lit_Up

So recently my shower has started to lose temperature. Whereas before it would get really nice and hot, it now gets no more than lukewarm and keeps getting cold again several times during a shower. Why is this, how can it be fixed, and for how much? My boiler is also losing pressure, but apparently the two are unrelated.

macman

In the absence of a crystal ball, it would help if you told us the make and model. If it's an electric shower, then it is indeed unrelated, as an electric shower is fed off the rising main and heats the water in the shower unit.
Assuming electric, if the flow is obstructed then the safety mechanism will cut the power, so I'd start by descaling the head and hose. Or it could be a thermostat problem.
What are you doing about the boiler? Pressure loss on a combi indicates possibly either a leak on the CH circuit or a sticking PRV-is water discharging fro the overflow pipe?