If it is truely heating all the time, I would suspect a hot water leak somewhere. Maybe the temperature/pressure relief valve is leaking…Find it on the side or top of the heater and see it its drain tube is hot. Or maybe there is a hot water leak under the house. You might feel the hot water pipe where it leaves the heater to see if it gets cool after not using the heater for many hours…Like overnight. If it is always hot, there may be a leak somewhere.