Question: I have a 2002 Sandpiper and the hot water is only luke warm. I have no manual and can’t figure out how to turn it up.
Answer: Why not contact the manufacturer of the RV or the hot water heater, to ask if you can adjust the temperature and how to do so. Perhaps they can provide a manual.
If your hot water heater is running on electricity, then it could be that the heating element needs to be cleaned and/or you need a new anode. If it is running on propane, then perhaps the flame needs to be adjusted. Just a few thoughts. Other comments welcome.