Blower will not shut off unless I turn off the power supply. It's a Snyder General mod.# GUG070A012N and is about 20 years old. Consequently, when the room reaches the desired temperature as set by the house thermostat, the burners will shut off but the blower still runs forcing cooler air to flow into the house. I suspect that the fan/limit switch is at fault and will have to be replaced. Is my assumption a correct one? My thermostat is set on auto and has been working correctly until a few days ago when I first noticed this problem. Any recommendations would be appreciated.

Thanks, Jim

Its not uncommon for a fan/limit control to stick first part of the heating season. If it keeps it up you will want to replace it. Any universal control will work, you will just need to give them the element length.