I have the same problem with my thermostatic crosswater valve, and wondered whether you managed to solve your problem, aside from turning up the temperature of the hot water?
Would be grateful if you could share your experience.
I have the same problem. I have two bathrooms both supplied from a pressurized system (no pumps).
When I first came across this problem I swapped the internal cartriges over and the problem moved over. So contacted crosswater and they supplied a new cartrige. Problem solved Both showers now run hot.
unfortunatley I now have the same problem on the shower with the old cartridge. I wondered if the cartriges have a design fault. It seem pointless renewing this cartrige only for it to re-occur.