Furnace overheating. Runaway condition?
Yesterday when arriving back home I found the house a very warm 80 degrees, but thermostat was at the lowest setting.
Old (20 yrs) Payne 100FAU-12, natural gas.
Opened closet where the furnace is located and noticed strong overheating smell.
Shut off gas supply, and later turned gas/pilot valve to off.
Gas company guy arrived and wanted to light pilot, but when he turned gas supply on, burners had gas pouring out with the pilot valve to the off position. He disconnected supply and capped it.
Out of work and cash is nearly non existent. Suggestions? Trouble shooting ideas?
Thanks in advance.

You need a new gas valve which is easy to change and cheap. Remove the old one and take it to a parts house and match it. Put it back on with a little pipe dope and you are all done.