I have a Baxi Duotec 2 40 GA Combi boiler 8yrs old and Hudson Reed Exposed Shower. Recent problems with temperature fluctuations in the shower. It will be warm for 5 minutes then it goes cold for 3 mins then hot again, you get the idea. Have massive problems with Limescale, a water conditioner is my next project. I have recently had a new Diverter valve, and new DHW heat exchanger fitted to the boiler. In addition I have replaced the thermostatic cartridge in my shower and yes it is plumbed correctly with hot on left and cold on right and the cartridge was inserted correctly. System pressure also correct. Im still having the same issues with shower temperature fluctuation and will test the NTC temperature sensor with a multimeter tonight. No Fault codes displaying and CH is fine. Is there anything else I am missing other than the above, and help would be appreciated