When your furnace won't turn on no matter how cold it gets, there are several troubleshooting steps you can take before you start looking up who to call for repairs. These don't require a lot of technical skill or much effort, so it's worth taking a few minutes to see if the problem is something you can fix yourself. Here's what to do.

Troubleshoot Your Thermostat

In many cases, your furnace may be working fine but simply not turning on. This can happen if your furnace isn't getting a signal to turn on, which can often happen if there is a problem with your thermostat. There are a few different things to check to make sure your thermostat is working correctly.

If your thermostat isn't connected to your home's power, try replacing its batteries. Batteries in a thermostat don't need to be replaced often, but if it's been a few years, your thermostat may simply not have any power.

If you have a thermostat that connects to WiFi, check to make sure it's currently connected. While this won't prevent controls from working at the panel itself, it will stop any other smart device from being able to control the temperature.

Check to make sure that not only is your thermostat set to heat, but that your fan setting is set to "Auto" rather than "On." The "On" setting will cause your fans to blow air whether or not the furnace is on, causing cool air to come from your vents.

If your thermostat doesn't seem to be responding even when it is connected to power or had its battery replaced, the thermostat itself may need to be repaired or replaced. Contact an HVAC technician for assistance.

Replace Your Air Filter

Your furnace requires a steady flow of air coming in from your house to function properly, and if its source of incoming air is stifled or limited, this may trigger one of your furnace's built-in safety features. With limited air flow, your furnace will have to work harder to heat the same amount of air, which can cause your furnace to overheat. To prevent this, your furnace will shut itself off once it starts to overheat. If you have a very dirty filter, this can happen quickly.

Check your air filter to see if it's dirty. If it has been a few months since the last time you replaced it, and you use your HVAC system constantly, it's likely your filter will need replacing. If you don't have any replacements on hand and aren't sure what you need, you can take your old filter or a note of its measurements to a hardware store to buy more. With regular use, it's a good idea to replace your filter every one to three months depending on the material your filters are made of.

Check Your Power

One thing that can prevent your furnace from turning on is a lack of power. If the rest of your house has power, this doesn't necessarily mean your furnace does; because of the power requirements, your furnace probably runs on a dedicated circuit, which means that you may not notice any problems with the circuit until you try to use the furnace.

First, check your circuit breaker panel to see if any breakers have tripped. If one has, and it continues to trip even after being reset, this can indicate an electrical problem that needs immediate attention. Don't try to keep resetting the breaker until an electrician or HVAC specialist has come to take a look.

Second, check the furnace unit itself. Most have disconnect switches of their own, which are often used by technicians when doing maintenance or repairs on your unit. If for any reason this switch is set to off, your furnace will not turn on even if the circuit and everything else is fine. If you don't know exactly where this switch may be, check the manual for instructions.

If everything is set properly and your furnace is still unresponsive, it's time to call a furnace repair contractor so they can take a look for you.