We have a hot water heater that was working totally fine. Then suddenly one day, boiling water would come out when the hot water was turned on. Later that day, we had no hot water at all. It was just lukewarm.
We reset the hot water heater and it worked totally fine and normally for three days. Now it's putting out boiling hot water again.
I looked it up online and it says maybe the thermostat. But I feel like it wouldn't have worked fine for a few days if it was the thermostat. But admittedly I'm new to ownership and don't know a whole lot.