Shower goes from hot to cold - changed thermostat in shower bar, Worcester combi serviced last year

Hello, firstly I'm not a qualified plumber but do allot of basic plumbing and hopefully I can help. I think your Shower has an anti scald valve which over time they scald up and corrode and stop working well. One way to check is to flush the toilet nearest your shower or sink while the shower is running and see if the water changes temperature. If it does I think that's your problem . I'm pretty sure they can be changed. I hope this helps , and apologies if I'm way off the mark .

Hi, just a quick check of your domestic water temperature may help. Your hot water needs to be set to 60 c lor less, sometimes the thermostat in the shower valve may open and close for protection. Also it may be an idea to install a combi mate valve to your shower feeds. Hope this helps

If you have already changed your thermostatic shower cartridge and you still have intermittent hot water, it will be your boiler fault, if a combi it can be the secondary heat exchanger partially blocked , or temperature sensors on your boiler.