When your heater isn't generating hot air, you might be dealing with one of the many common furnace problems. Consider the following furnace troubleshooting tips:
Make sure your thermostat's fan settings are set to "auto" rather than "on."
Check to make sure no one else has lowered the temperature on your thermostat.
Replace any dead or damaged batteries in your thermostat by checking the batteries first.
Clean each part of your furnace, paying close attention to the parts that are more likely to accumulate dust and dirt. By hiring HVAC experts, the system could also be thoroughly cleaned.
Check to see if the gas valve is open and check to make sure that it is unobstructed.
Shut the blower motor panel after performing any maintenance or repairs.