No heat
Check the breaker, the thermostat setting and whether the timer has run down. If the breaker trips again, stop and call an electrician.
Heater works but the cabin stays cool
Check the door seal, the vent position and the room temperature. A cold room and an open vent will keep a small heater behind.
Control panel errors
Photograph the code before resetting. The seller will ask for it.
When to stop
Cut power if you smell burning, see a spark, or the panel is hot to the touch.