Decoding the Blinking Green Light On Your Furnace

Furnaces are usually tucked away. Hidden behind a closet door or forgotten about in a basement. So seeing a blinking green light on your furnace may seem out of the ordinary. There are several lights that your furnace could have. Usually, the colors are red, yellow, or green. 

Common reasons your furnace has a blinking green light are that the furnace needs a reset, won’t ignite, the furnace is on but there is no request for heat, or the thermostat is broken. A flashing green should not be ignored and may require attention from a professional. A red light on a furnace means that your furnace is not receiving power. 

Furnaces have their own way of communicating with us. If you do not understand the communication then you could be at risk of causing more damage to your furnace. I didn’t know what to do either when I first saw my furnace blinking green. Now I’m here to help you understand the language of a furnace.

Common Error Codes For Furnaces

Soft Lockout: For example, pretend the ignitor on your furnace has burned out. If you try to ignite the furnace and it fails three times in a row then the furnace will go into a soft lockout. So for the next three hours, it will do nothing. After three hours it will restart and try again.

Hard Lockout: A hard lockout is what happens after a soft lockout. As the furnace keeps trying to ignite it will reach its maximum allowable attempts. Your furnace will completely shut off and not try to start up again. The only way you can turn it back on is by turning the power off and on.

Flame sensor error code: This code usually means that you need to clean the flame sensor. If cleaning does not work then there may be a bigger issue with the flame sensor.

Limit switch: Shuts the furnace off if the furnace overheats.

Flame rollout: Shuts the furnace off if the combustion fumes are coming back into the burner box.

Ignitor failure error code: This could mean your ignitor has burnt out or it is not getting power from the control board.

Pressure switch error code: A pressure switch is a safety switch on the furnace. If it detects something wrong with the combustion fumes it will turn off the furnace.

What Does A Green Light On My Furnace Mean?

A green light on your furnace can mean that there is a problem with your furnace. There are a few common problems the furnace has when the light is blinking green. Some are that the furnace needs to be reset, the request for heat has failed, or there is an issue with your circuit board.

The sequence the light flashes in will indicate what is wrong. Your furnace may blink different colors other than green. If so, it is best to check the user guide about the flashing lights. You should pay attention to the green light because your furnace can get severely damaged if you don’t.

Is Your Green Light Flashing in a Sequence?

To check if your green light is flashing in a sequence you’ll have to pay close attention to the light. Sometimes the light is located at the bottom or the top of your furnace. Locate the light then count the number of flashes. You should watch it several times to make sure you don’t miss count.

The most common solution is to reset the furnace. You should reset the furnace before you do anything else. If the furnace turns back on and ignites then it just needed to be reset. However, if the light is still flashing you’ll need to find the error code.

To find the error code you have to find your installation manual. The meaning of the flashing sequences will be in the manual. If the light sequence is indicating something is wrong, you’ll need to call a professional. They will be able to access the furnace and fix the issue.

Is Your Green Light Blinking Slowly?

A slow blinking green light means there may be something wrong with your furnace. You will easily be able to tell if the green light is blinking slowly. It will fade in and out slowly. While a fast-blinking light will blink rapidly.

A possible situation when the furnace has a slow blinking green light could be if your furnace is on and you haven’t requested heat. This is a problem because if you do not request heat, then the furnace should be off. You may need to reset the power.

Another possible situation where the light blinks slowly is that there is something wrong with your furnace circuit control board. This could be from a loose wire or the whole circuit board may need to be replaced.

To fully understand what a slow green blinking light means on your furnace, you will have to look at the manual of error codes. This is because every furnace is different and the light could mean something else. 

For example, there could be a thermostat malfunction which is one of the most common issues. Along with possibly a tripped circuit breaker, a blown fuse, or there could be something wrong with the furnace’s pilot light

What To Do If Your Furnace Has a Green Flashing Light.

When you see a green flashing light on your furnace do not panic. You can check the furnace out yourself before you need to call a professional. Chances are you just need to reset the furnace. However, there is a possibility that there is a bigger issue.

You should start by restarting your furnace. If it’s still blinking after you restart it then it’s time to find your installation manual for the furnace. It will have all of the error codes and tell you what the light sequences mean.

Look at the light carefully. Try to decipher whether it is blinking slowly or quickly. Then count the sequence. Count it over several times so that you know for sure what code is blinking. Try to match the sequence and speed to the manual’s error codes.

Once you have figured out the issues you can decide if you need a professional. It may be an easy fix such as cleaning something. If the reset did not fix to furnace then you should call an HVAC contractor. They will be able to safely fix the problem with your furnace. Depending on the problem, the cost of a contractor can be anywhere from $100 up to thousands. 

What Happens If I Ignore The Flashing Green Light?

Ignoring the flashing green light on your furnace will only cause you more issues. It is best to not ignore the light so you won’t have to deal with a build-up of problems. Ignoring the light may also compromise your comfort. The ICF board could start making loud noises or your blower may constantly fail to run.

For example, if your furnace has a broken component and you ignore the light, your furnace could end up completely breaking. Meaning that you would need to get a new one. A new furnace is much more expensive than repairs.

Another consequence of ignoring the blinking light is that your utility bill could significantly rise. Your furnace will have to try to run extra hard to run at full capacity if it is damaged. This is because it’s trying to compensate for an issue so your bill will skyrocket. 

When Should I Call A Professional?

You should call a professional when you cannot figure out the issue or the furnace needs a repair. The HVAC contractor will without a doubt find the issue. They will tell you what is wrong and what they need to do to fix it. If you assess the furnace yourself and call for a specific issue then you will get a professional that can do the fix.

HVAC contractors are professionals on furnaces and your whole HVAC system. They know what error codes are, how to fix them, how to properly test a furnace, and how to replace a furnace if necessary.

The cost will highly depend on what is wrong with your furnace. An assessment will cost around $100. During the assessment, they will go through a checklist of possible problems until they find out what is wrong. 

Where it can get costly is when your furnace needs a big repair or a replacement. To replace a furnace the price could range from $3,000 up to $7,000. Repairs may vary from $100 to thousands. An electric furnace is also cheaper to repair or replace than a gas furnace.


A green flashing light on your furnace means that there is a problem. Whatever the problem may be, it should not be ignored. It is easy to forget about your furnace because they are hidden away. Resolving the problem will ensure no other problems will arise. 

The most common solution to a blinking green light on your furnace is restarting the furnace. Just like your wifi, sometimes they need to be reset. Another common solution is to check what the green light means and fix it yourself. However, this may be difficult if you have no experience. If you find the job is too big for you then you should call an HVAC contractor.

It is easy to forget about your furnace. Try to check on it every once in a while. It could save you from possible issues in the future.