Performed heater diagnostic on 2020 Lennox Unit. Upon arrival homeowner stated that just about a week ago he noticed that the system continuously runs in fan mode and does not produce heat. During the troubleshooting I noticed initially that to the burners Appear to be orange and not burning properly. Also noticed rat droppings inside of the Furnace closet area. At this time it appeared that oxygen was not being supplied properly to the propane burners Resulting in a hard lockout causing rollout switch to be tripped. Previously the original Heater was also clogged up due to rats making it their home and stuffing debris inside of the heat exchanger Resulting in a similar problem. Also main door that covers up the furnace has no air circulation for oxygen the flow recommend that Louvers are added to increase Airflow to Heater. At this time burner Flames look healthy and blue. System is Heating upon departure