i have a two year old tempstar furnace that now & then just decides to shut down. i can get it to restart by throwing the circuit breaker or just flipping the switch on the furnace off then on again or i can lower the thermostat below the current room temp. and then when i saise it back above the current room temp. the furnace will kick in and start. the co. that installed the furnace do not know what's going on.

Try to clean flame sensor. Do search on this board.

As well, look for an error code flashing and count the flashes, refer to the chart on the back of the bottom furnace door cover. The error code ( blinking LED on either the gas valve or fan control board ( depending on which ignition system you have) will guide you to what the unit failed on.