Hello. My mixer shower (non-electric) recently started running luke warm. I know this can happen at this time of year over winter but I've been in the property over 10 years and it's never been this bad before. The combi boiler was checked and is ok. The hot water from taps is uneffected and very hot. I replaced the thermostatic cartridge (ceramic) and it made a very small difference but nowhere near back to normal. I had to turn off the water at the main stopcock to do this work and was wondering if the pressure from the mains, if I increased it during the work, could contribute to the luke warm water? If not then does anyone have any other suggestions? Thank you so much for reading this.