thermostatic cartridge

Hi, My shower thermostatic cartridge is faulty I believe, as I can only get lukewarm water and no hot water. I have tried removing it to see if I can get a replacement online but I am stuck at this stage (pictures attached). I don't know the brand of the shower mixer. Does anyone know how I can...

I have an old Worcester Bosch Greenstart HE plus combi boiler. 3 months ago the shower, which has been working perfectly for last 5 years, would start off at correct temperature and then after about 2 minutes would run cold. Just as it was running cold I heard the boiler fire up and after...