Arrived to find furnace in lockout due to not registering a flame. Checked flame safety sensor to find it failed and not registering flame. Replaced flame safety sensor and tested operation. Talked to tech support as we have had this problem here previously. I performed several tests to make sure it’s not an issue with the equipment. Ground and voltage testing where it should be. Tech support and I came to the conclusion that something in the environment is coating sensor and ruining it. Combustion air intake runs into attic and I am unable to see where it comes out. We recommend running a new combustion air from mechanical room to side of garage so we are able to bring in fresh air and help prevent this issue from happening again. Quote is attached.