Our LP gas furnace seems to be cycling rather quickly. The exhaust blower will come on for a few seconds, then the burner ignites properly. When the main blower fan kicks in the burner shuts off immediately. The blower continues to run for 30 sec. then stops. The exhaust blower continues for 45 seconds. Then it stops as well. Three to five minutes later, depending upon air temps, it all repeats. This does not seem normal. It is a down-flow York Stellar air handler/furnace. I suspect the supply air high limit switch.

Check and clean the flame sensor and pilot orifice.

Check to see if the flame is blowing away from the flame sensor when the blower comes on. If so you have a bad heat exchanger or burner inlet plate. A semi restricted vent will let the burners light but the pressure switch will open and lock the flame out. A dirty flame sensor will lock the burners out in around 3 seconds. How long is your burners on before the blower comes on?

Check to see if the flame is blowing away from the flame sensor when the blower comes on. If so you have a bad heat exchanger or burner inlet plate. A semi restricted vent will let the burners light but the pressure switch will open and lock the flame out. A dirty flame sensor will lock the burners out in around 3 seconds. How long is your burners on before the blower comes on?

The flame does not move away from the flame sensor when the blower comes on. The flame goes out immediately upon the start of the main blower. The flame sensor is clean and properly placed. The burner is lit for 30-40 seconds before the main blower starts and the blower remains on for 45 seconds following flame out.

The blower will come on after any fault or failure, so now we need to find out why the burners are faulting out. Did you check for a restriction in the vent(connection point on the furnace) or vacuum lines going to pressure switch, if 90% furnace restricted condensation drain line.