I have an older Rudd furnace (at least 20 years old) and it went out yesterday. A handy man came and replaced the thermostat, then the transformer and then the thermocoupler. After he replaced the thermocoupler the furnace came on and seemed OK. After he left the furnace went off again. I went out and his the reset button and it came back on, but only for about 5 minutes or so. I hit reset button again and it came back on, but again went back off after a few minutes.

Where exactly is this reset button?

I agree what reset button are you resetting? It also seems like he replaced to many parts since usually only one part fails at a time.