If your furnace is not turning on, the first place you should look isn't your furnace itself; instead, you should look at the thermostat that controls your furnace. Your thermostat is responsible for conveying information to your furnace and for telling your furnace when to turn on and when to turn off.
When your furnace isn't blowing out heat when you think it is, your best bet is to spend some time checking out the thermostat first.
1. Check the Heat Switch
First, you need to check and make sure that the switch on the thermostat is turned to heat. It is not uncommon for the switch or setting to get turned to cool or to the fan setting accidentally, leaving you wondering why your furnace is not blowing out hot air. Make sure the thermostat is actually set to the heat setting.
2. Check the Temperature
Next, you need to check the room temperature on the thermostat and the temperature settings. If the room temperature is within two or three degrees above or below the desired temperature, your thermostat may not cause your furnace to turn on.
If you want the furnace to turn on, set the desired room temperature so that it is at least five degrees warmer than the actual room temperature. If your furnace is working correctly, this should activate your thermostat and turn it on.
3. Check the Programming
After that, check the programming on your thermostat. If you have a programmable thermostat, you may have set the temperature settings such that your furnace wouldn't have a need to turn on right now. Make sure that the programming is right, and that your thermostat is showing the right time of day. For example, if the a.m. and p.m. settings were flipped on your furnace, the programming would be off.
4. Clean the thermostat
Next, you need to make sure your thermostat is clean. If your thermostat is dirty and full of dust, it may not be working right. You can dust off your thermostat and use a little forced air or a handheld vacuum to clean up around the thermostat. Make sure the thermostat is firmly attached to the wall as well, and that the wires are not loose.
If you have a furnace in your home, and it isn't working right before you start tinkering with the furnace, check the thermostat and make sure the issue doesn't rest in the thermostat. The thermostat controls your furnace and is the first thing you should check when your thermostat doesn't seem like it is working properly.
For help with a furnace repair service, contact a professional near you.