All right, I'm a total rookie, but I enjoy troubleshooting (and hate spending money I don't have to) so I'm trying to figure out what's going on with our furnace. We have a Ruud electric ignition gas furnace (UGDA-10EC-ER), which as far as I can tell is about 20 years old. It's certainly rusty enough to be that old. Not sure when the last time it's been inspected.
About a month ago we started having issues where the furnace would operate fine all day, but when we woke up in the morning, the house was cold and below the called-for temperature on the thermostat. I narrowed it down to what I thought was the problem...I discovered the limit switch, and when I would push the manual button in and then pull it back out and turn the power back on, the pilot light would kick on, the blower would come on, and everything operated normally. Until a night or two later when it would do the same thing. Each time, I would just go reset the switch and it would work again.
I did some research about what the limit switch did, and that it was getting too hot in the plenum. Possible causes were lack of intake air, and closed registers. We only have 5 registers, so I made sure they were all open. We only have one return air vent, so I made sure that was clear. I replace the filter regularly, so it wasn't that.
Well, now it's to the point where even during the day, it will go on for about 5 minutes and then shut off. I will go down, and even without turning off the power, hit the side of the furnace (professional, I know), and the flames will pop on, the blower will come on, and it will heat for about 5 minutes, and then shut off again.
So now I'm wondering if it's a faulty connection somewhere? Or I read something about the valve for the gas not staying open?
Any thoughts? I live in Michigan...and it's January...so it's cold!