I have a Cifial thermostatic shower valve that is not adjusting the water temperature at all when the knob is turned. I took the unit apart and couldn't find anything that was glaringly wrong but I am not experienced in plumbing, I was mainly looking to see if anything was stuck. Could this be a bad cartridge? I live in an area with hard water but I have a water softener installed now but I can't speak for how it was working before I bought the home, I am wondering if perhaps soaking the cartridge in CLR would help. Any ideas of what could be wrong? I would prefer not to buy a new cartridge if that's not the culprit since they are quite expensive for this valve.
Picture of similar valve: