Recently been having issues with my Goodman GMT070-3B, with it lighting and staying lit. I spent last winter lighting it manually. When it reached the thermostat temperature, it cut off and I'd have to start it manually again. I've recently replaced the flame sensor and ignitor. Everything starts up fine now. But the flames go out after approx. 3-5 minutes, and the heater restarts the cycle all over again. I don't know what else to trouble shoot. Any suggestions would be appreciated?

Sounds like a limit switch that would shut the heater off if temp in the heat exchanger gets too high. I would first look at an air flow problem. Filters, flue blocked by bird's nest etc...

Thanks. I replaced the filter and checked the flue, all clear. Unfortunately I ended up having to spend $106 to have a tech come look at it. I was told that I had a bad heat exchange and that the air pressure switch was shutting the heater off once it sensed the bad heat exchange. YOU WERE DEAD ON! Wish you responded a little earlier. Lol I was advised that I'll need a new heater. So now I'm shopping around for a good heating manufacturer and a honest, trustworthy, knowledeagable, professional installer.

Thanks. I checked the air pressure switch and couldn't find anything wrong. I also replaced the filter and checked the flue, all clear. I ended up spending $106 to have a tech come out and tell me that I have a bad heat exchanger and the air pressure switch was sensing the bad heat exchange and kept cutting the heater off. YOU WERE DEAD ON! I wish you would've responded a littler earlier. (lol) I was advised that I should just get a new heater. So now I'm shopping around to find a reliable manufacturer and a honest, knowledgeable, and professional installer. Any suggestions on a good heater?