Furnace Codes: What They Mean and How to Fix Them!

When you first get a new furnace, it’s exciting. It’s something new, something with the potential to help heat your home more efficiently and save on your heating bill. That said, furnaces can be tricky things. They have an array of sensors and codes to check their performance, and if any of those don’t work as advertised, you might run into problems. How do you know what these error codes mean? Do you need a repairman to walk you through everything or can you handle it on your own? There are many troubleshooting steps for repairing most issues – we just need to know which one applies in our specific case! Fortunately for you, we’ve compiled this list of common furnace codes and how to fix them:

Check the filter and clean the condenser coil

Furnaces have filters to help keep them from getting clogged, but that filter still needs to be cleaned regularly. If yours is particularly dirty, you may encounter a code. You’ll want to clean the filter and, if necessary, replace it. If you have a gas furnace, you’ll also want to clean the condenser coil regularly. That coil is what helps your furnace heat up and stay clean. It also keeps it from overheating and causing a fire. If it gets clogged, you’ll need to clean it out. You can clean the filter and the condenser coil using a vacuum or your garden hose. Be sure to unplug the furnace before you do!

Turn off your thermostat for a few hours

If your furnace is short cycling – that is, turning on way too often – and you don’t want to take a look at the filter or anything else, you could try turning off the thermostat. If you turn it off for a few hours, the furnace won’t be able to reach the temperature you set it at, and it should go back to cycling correctly. Turning off your thermostat can also help if your furnace is running too long. It’s possible the furnace is sensing what it thinks is a cold home when it’s really warm inside. If you turn off the thermostat for a few hours when it shouldn’t have been running, it may learn that reality and start behaving itself.

Check the gas pressure

If your furnace has a pressure switch, you may see a pressure code. If the pressure is too low, the furnace won’t be able to function properly. In that case, you’ll want to check your gas pressure. You may need to call a repairman to do that for you, but it’s pretty easy to check for yourself. If you have a gas furnace, you’ll have a pressure regulator. You’ll want to make sure it’s not set too low or it won’t be able to pressurize the system correctly. If it’s set too high, it can cause an over-pressure situation that can lead to a fire. You’ll be able to see the regulator and know what pressure it’s set to. If it needs to be adjusted, you can turn the screw to change it.

Check the flame sensor

If you have a gas furnace, you may see a flame out code. If the flame sensor isn’t working right, the furnace won’t be able to stay on. You can check the flame sensor to see if it needs to be replaced. If it does, you can replace it yourself, though you may want to call a repairman first to make sure you’re doing it right. If you have a propane furnace, the flame sensor should be mounted just above the burners. If you have an oil furnace, the flame sensor should be mounted above the oil burner. If you have an electric furnace, the flame sensor should be mounted above the blower. If your furnace is seeing a flame out code, you may just have a bad sensor. Replacing it should solve the issue, but you’ll want to make sure it’s installed properly.

The motor constantly turns on and off, doesn’t stay running, or makes clicking noises

If your furnace motor is making a lot of noise, or it’s turning off and on like it’s having a fit, that may be because it’s overheating. You may have something blocking the fan or it just needs to be cleaned out. You can check to see if there’s anything blocking the fan and clean the furnace as necessary. When the motor stops running, that may be a thermal overload. If your furnace has an overload, it will shut itself off if it’s too hot. You can reset the thermal overload by turning off the circuit breaker or removing the fuse. You may have to have a repairman come out if it keeps happening.


Furnaces can be tricky beasts, and when they aren’t working correctly, it can be frustrating. Thankfully, most issues are easy to fix, and there are plenty of troubleshooting steps you can take to try and fix them yourself. If you’re unsure what the problem is, call a technician. They will be able to help you figure out what the issue is and repair it quickly.