Hello, I am having problems with my furnace. It just stays on. The t-stat seems to have no control on the furnace. I actually disconnected it and the furnace still just keeps running. It's a slant fin furnace with a beckett oil burner model AFG. If that helps at all. The only way to control it is to turn off the master switch. I usually turn it on for an hour or two then off till needed again. Thank you for any info.

Disconnect one of the thermostat wires from the burner control. Usually a R red or W white wire will do. If the unit stops running you have a thermostat wire or thermostat problem. If the unit keeps running after disconnecting one of the thermostat wires then you have a burner safety control problem.