Burner short cycle..
Ductwork air blockage..
Did you shut or block off any ductwork registers? Blockages or intentionally closed off vents slows the air flow going across the heat exchanger, this increases the temperature until the over temp safety trips the burner off until the temperature drops to a safe level.
Fan running too slow..
Check your battery voltage at the battery and at the furnace. Since the fan motor is DC it runs directly from your battery and when the battery voltage sags, so does the motor speed and the reduces the air flow causing high temperature safety to trip and turn off the burner.
Too much propane pressure..
Regulator malfunction can result in higher propane pressure to the furnace which affects flame size.. Check the burners on your stove, flame should not be excessively high and should be all blue.
