I don't know whether it's down to either of these reasons, unless the pressure fluctuates, because it isn't constantly cold it's sporadic and lasts for about 30secs each time - which is a long time when you're trying to have a hot shower on a cold morning!
I had a Triton Nene Thermostatic Standard Bar Mixer Shower (I think) installed 2 years ago. It's generally worked well, but over the last few months it has started getting cold more and more frequently during a shower, even though the thermostat control has not been touched.
Can anyone...