I came to home for a no heating service. I set thermostat to heating mode and started diagnostic. Furnace turned on and burners ignited. I never got any error codes and had heating on. I recommended a maintenance agreement to stay on top of systems. I began my maintenance on furnace, I cleared pressure switch tube. Blew out all debris out of tubing, I cleared ports on both ends. Cleaned inside and out of furnace with my brush. Deep cleaned the flame sensor because it was caked on with brown corrosion. Filter was replaced by myself last visit.