Performed diagnostic on 20 year old furnace. Homeowner states that furnace is not heating well. They had a guy come out for an AC maintenance in the summer time and he told them that their system was old and unsafe To use, and that they should just replace it. Homeowner called us out today for a second opinion. Had homeowner cycle the system for heat. Furnace kicked on and started heating. Took temperature rise and static pressure and both were high. After about 5 minutes of running the system shuts off And then reignites again after a couple minutes, meaning that system is getting too hot and short cycling. This is why it is not heating well due to half of the time that it is running the flames are off and it is not heating. Also performed safety inspection to verify what homeowners were told on maintenance visit which was done by a different company. Pulled blower wheel off to inspect heat exchanger. Found a number of very concerning hot spots, with one in particular on top of the fi