If you're having trouble with your furnace or heater, here are a few troubleshooting tips to try before calling a professional for repair. Check to ensure the thermostat is working and turned to “heat”. Ensure there's power to the furnace/heater. Check air registers and grills to make sure they're not blocked and are open and blowing air. Check to see if your filter needs changing. Check your pilot light and use your owner's manual for instructions on how to relight it. If the tips mentioned above aren't helping, call a professional.