Client stated no heating -I found furnace non operational -Filter was extremely dirty and plugged up, client provided filter and replaced it -All vents are open in the house -It appears that high limit switch was tripped, and it seems to be due to a lack of airflow and the filter was completely plugged -Heat rise with new filter in place is remaining steady at 70° -Furnace has been running for over 30 minutes and heating the house -A maintenance membership was highly recommended to take care of this older furnace and make sure filter is being replaced each visit