I can't remember what brand my old heater was, it was all black and it had the green and red lights. At first it was constant red and then the green would turn on when it was up to temp. Then it started flashing, red for a minute then green and kept flashing. I finally got a recall notice in the mail about the heater. Didn't say what was wrong with it, but I'm pretty sure that was it. It usually has to do with the thermostat breaking. Most use cheap kind.. It should still heat but doesn't automatically shut off when done getting to the temp and them your tank gets to hot.