It is getting a little chilly at night, so you decide to turn on the furnace. But it won’t ignite. What’s going on and how do you get your gas furnace going again? If this is an emergency and you absolutely need the heat, it’s probably best that you just call an HVAC technician to get them on the road to you. But if you have the time and inclination to troubleshoot your furnace yourself then there are things that you can look into for yourself. We’ll walk you through them below.
Check your Thermostat
Yes, the most likely reason that your furnace isn’t lighting has nothing to do with the furnace itself. The thermostat should be your first stop on your quest to figure out why your furnace isn’t working. Thermostat problems are typically easy for homeowners to spot and fix. For example, the most common issue is that the thermostat isn’t actually set to heat. Without that, the furnace doesn’t even think it should turn on.
So, take a look at your thermostat. Is it set to heat? Is the fan on? Is the temperature in the home so cold that the thermostat would trigger the furnace to turn on? You can set the temperature higher just to make sure that the furnace will indeed respond to the thermostat. Then, set it back down to your preferred temperature.
The Pilot Light or Ignition Sensor
Once you’re sure that the thermostat is telling the furnace to turn on, then you can start looking at the furnace for possible reasons that it won’t start up. One of the most common problems is that the ignition sensor will not turn on. If you can hear a click from the furnace, that is the signal from the thermostat reaching it. Then the ignition sensor should start things up, but if the sensor is dirty or broken, it won’t work.
You can check the sensor for yourself. Turn off the power and gas to the furnace first, for safety. Remove the panels and look for the ignition sensor. Once you spot it, you should be able to see whether it’s dirty. Remove it with a screwdriver and clean it gently. This is a delicate part so be sure not to break it. Then you can restore the furnace to how it was and see if the problem is fixed.
If not, the sensor may be broken instead of dirty. An HVAC professional can confirm this for you and replace the sensor if warranted.
The Power Switch
Rarely, but sometimes, you or an HVAC professional may have accidentally switched the furnace off using the switch inside the machine. Even gas furnaces have to be connected to the electrical system to work, and this switch allows that connection to be turned on and off. So, take a peek inside the furnace, while it is off, to see if the switch has been left off. You can also check to see if the breaker for the furnace has been tripped. If both are fine, then you know the problem isn’t the supply of electricity to the furnace.
The Gas Supply
Of course, the furnace also needs gas in order to ignite. There are a few different spots in the gas line where something may have gone wrong and prevented the gas from reaching your furnace. First check the gas valve closest to the furnace. Has it been partly or fully closed by accident? Open it up if so.
If that is not the problem, then you can check the home’s own gas line valve, which is outside. Perhaps something closed this valve. However, if it is also fine then you can check to see if gas is actually making its way into the house by trying to turn on another gas appliance, like the stove. If it turns on then potentially there is some other problem with the furnace. If no other gas appliances will turn on then the problem could be a gas leak. This is a safety issue, so reach out to an HVAC professional and evacuate from your home, just in case.
There are many other potential causes when your furnace won’t turn on. What if you can’t figure out why your furnace isn’t lighting? Or you don’t want to walk yourself through these steps? No problem, at Thompson Plumbing Heating and Air Conditioning we are here to help. You can reach out to us for any furnace problems that you have.