Performed wall furnace diagnostic, 20+ yrs old Williams doubled sided wall furnace. Not heating, found the gas pilot not on, tried lighting won’t stay on. Took out the thermalpile and cleaned it. Then or it to stay on, didn’t come on right away. With thermostat on unit should have fired right away had to jumper it at gas valve to get unit to lite. House was cold so let system run for 30 mins before adjusting thermostat to see if it working correctly. Found one of the screws that holds the burner in place loose. Found safety switch has metal connections not covered. Covered them but as the line moves the unit turns off loosing the pilot. Recommend due to age replacing unit vs repairing. Going with the repairs today, trying to get it to last thru the end of this yr.