Hot water in Mixer Shower only warm.

[russ026]

I have a thermostatic mixer shower runner off a combo boiler. It used to give great hot showers (almost boiling on the hottest setting). Recently we only could get cold water from the shower. I asked a friend who knows a bit about plumbing. He said it sounded like the cartridge was broken. I replaced the cartridge and the shower gives hot water again However it is not as hot as it used to be. Still useable but nothing like it was. You have to put it on the hottest setting to get it warm enough.

Any ideas how I can get it back to piping hot again?
I’m wondering if the cold is just over powering the hot?

 

[Axel]

The relative position of the knob on the spindle of the cartridge, along with the end stops on the valve housing allow 'calibration' of the valve. This may help make it hotter. Also check the temperature of the hot water from the basin taps.