Could be a couple issues.
1) bad thermostat
2) bad circuit board
3) Sail switch no operating properly.
Since you did a reset on the thermostat, that is what I would look at.
Remove the cover to gain access to the wire terminals. If it is a two wire thermostat, connect the two wires together. The furnace fan should start right up and then in 10-15 seconds the burner should come on. If this happens separate the two wires. The furnace sghuld go into cool down mode and then shut off in 20-30 seconds.
If you identify the problem, maybe the dealer will send what you need and save a trip and hassle.
What is make and model of furnace?
What is make and model of thermostat?