The last couple of weeks I have had to reset the red button to get hot water. As soon as it is reset we have hot water. This morning no hot water. Same thing, I reset red botton and we have hot water. Do I need to replace the thermostat?

How old is the unit? Sounds more the element is going.

I agree. One of the elements is bad. Best to replace both at the same time. The bottom element usually is the culprit. That is where the sediment is in the tank and it corrodes the element.

I think we are all heading in the same direction. What brand and model is the heater?