We recently had a problem where our heater would just stop working and I would have to tap the panel door to the unit in the attic, and it would kick back on. I replaced the pressure switch after seeing the code flash on the unit, but that didn't fix it. I then saw the code for "High Aux or Spill Limit Switch Open" so I called a repair guy out and he never could find any problem. He tested and the wiring and cleaned all the connectors and it's been working for 4 days straight without a glitch. All of this has caused me to pay closer to attention to the unit and I've noticed that it cycles on/off quite a bit. I timed it and the flame kicks on for about 3 1/2 minutes and the blower starts about 15 seconds after it ignites and it stays on for about 6 minutes. Then everything stays off for about 5-6 minutes and repeats. It's set for an internal temp of 68 and it's been about 35-40 degrees at night lately.
I have the original thermostat (12 years old) and I've read about being able to adjust the anticipator but don't see anything like that on my thermostat. I found a decent thermostat at the hardware store that says you can adjust the swing to help reduce the amount of cycles. My question is should I just buy the new thermostat and increase the swing or should I have another repair come out and look for more problems.
It could be the tstat but the only way to know is to put a volt meter between W and C on the board when it is running and see if the tstat shuts off. Most units have the burner run for 90 seconds B4 starting the fan so you may want to check that again or have a different problem. I would buy a Honeywell Focus Pro tstat from HDepot and replace yours if it is that old. Average life of a tstat nowadays is about 10 yrs.
"Cut it twice and it is still too short".