Arrived onsite to investigate a no-heat issue on a York propane furnace. The furnace was off upon arrival. We turned the unit on and it initially fired and ran properly; however, after approximately five minutes of operation, it shut off and displayed a limit switch fault. Upon inspection, we found the air filter to be heavily plugged. A clogged air filter can restrict airflow and cause the furnace to trip the limit switch. We recommended replacing the air filter and performing an annual furnace tune-up. The customer stated they would obtain a replacement air filter. Performed annual tune-up, cleaned the burners, heat exchanger, igniter, and flame sensor. Checked all safety controls, condensate, venting, fans, and overall furnace operation. Bubble-tested the gas line and checked carbon monoxide levels — no leaks detected. Verified operation; system is running properly at this time.
