I noticed that my front room furnace burner seemed like it would cycle ON/OFF every few minutes, even though the temperature hadn’t come up to the thermostat setting yet. I made a note of it, but didn’t think much more about it until I read someone else was experiencing a similar problem and was floating the idea that it might be a bad temperature sensor on the heat exchanger.
This got me to thinking, If the heat exchanger is getting to hot, the temperature sensors job is to turn off the gas and allow the heat exchanger to cool off. This is exactly what I’m seeing. However, I took it a little further, what if there isn’t enough airflow across the heat exchanger to cool it and this is causing it to overheat.
My front-room furnace feeds 5 vents from a plenum, four of these are the round adjustable like the ones from e-trailer shown in the photo. When I looked at the vents they were all closed, I figured I just discovered my problem so I opened them. I turned the furnace on and when I went to check airflow from the vents, they were all closed again. WTH. I opened them again and I noticed that the blower air flow from the furnace would push the little doors closed again. There wasn’t enough resistance in the little doors so they would stay open..
SOLUTION. I removed each of the vents and using a pair of wire cutters, I reached up inside the vent and cut off and removed the little louver doors from the vents. Now there was no way to close them and I’d have full airflow, all the time. Since I’ve done this, my furnace doesn’t turn the gas ON/OFF anymore, and I’m getting good heat in the front room area.