Ok, maybe I didn’t give enough info. The shower temp is controlled by one knob – turning right/left makes water cold/hot. The shower runs at the set temp for about 30 seconds before shooting out scalding water then cold water. The alternating hot/cold then persists throughout the shower. One hot water heater is used to heat 4 apartments, but is locked behind a door and I can’t get to it to find out any specifics. The building is about 25 years old and I would imagine it’s the original plumbing. My landlord has sent out maintenance 3 times, replaced the lower element, and done who knows what else, but the problem persists. Any suggestions will help at this point.