I replaced the shower cartridge in the upstairs bathroom with a new Delta cartridge because it was only supplying lukewarm water. After testing it, the water is now coming out hot. In the master bathroom, I replaced both cartridges and adjusted the scald guard to allow for more hot water. Currently, the water is quite hot but not hot enough for the homeowners. They mentioned that they remodeled their shower two years ago, so I recommended that they contact the general contractor who worked on the project. They should check if the contractor has any photos from before or after the remodel. Additionally, to further diagnose the issue, they will need to access the area behind the shower. There is a cabinet behind the shower, and they will have to disassemble it to allow us to cut into the drywall. This will help us determine if the plumbing lines were connected properly or if there is a crossover issue.