My water heater will over-pressurize and open the blow-off valve and begin spilling water to the drain in the utility closet. I've tried stepping down the temp. incrementally to find a position that it likes, but nothing acceptable for showers will be acceptable for the heater. We've since been turning off the water supply valve to keep it from overflowing when we're not in need of hot water.
I called a plumber and the guy mentioned that they keep cranking up water pressure through our area to supply the folks farther out with decent pressure. He was wondering if we had a pressure reducing valve in the unit and I was going to check on that before I had a plumber physically come out. I believe it is more a problem with excessive water pressure coming to the tank because if we shut off the cold water supply to the unit it will not spew water even with the temperature elevated.