What Does A Blinking Red Light On Furnace Mean?

Did you just come home to the furnace blinking red light? Maybe the furnace has been problematic recently, starting with difficulty and making weird noises when it runs. Or maybe the blinking red lights are out of nowhere. 

Now, you’re in a panic, wondering what the heck is wrong with your furnace. Does it put me in danger? Is it something I can fix myself? Or must I call the experts? 

Read on to find out common reasons for the red flashing light, what the light might be telling you, and the next steps to take. 

Should My Furnace Light Be Blinking?

Yes, if it’s ON, it will most likely blink. Most furnaces blink even if they’re in perfect working condition, perhaps so you can relax knowing that everything is fine. 

Generally, the furnace will blink a green LED light – and fast. So, if you observe the furnace blinking green lightfast and continuously (for as long as the heater is running), you don’t need to panic. On the contrary, you should be happy.

However, if it’s not blinking or blinking continuously but slowly, then you may have a problem. Typically, the only time the furnace shouldn’t be blinking is when it’s OFF. So, if it’s blinking when OFF, there’s a problem. 

A continuous but slow flashing green light is also often not a bad sign. All it tells you is that the furnace is running perfectly, but the thermostat hasn’t requested heating. Thus, it’s only an issue if you’re freezing on the chair/bed, but and thus, expect the thermostat to request heating. Could the thermostat be broken? Is it wrongly set or poorly positioned?

What Does a Flashing Red Light on the Furnace Mean?

It’s almost always a sign of trouble. Whereas the green flashing light can sometimes be good news, a red flashing light generally means that the furnace has run into a significant problem that requires immediate attention.  

The most common issues when the furnace LED light is flashing red include;

  1. Blower running after power-up: Whenever you restore the furnace, the blower will fire up, resulting in an error code. Don’t panic. Everything is fine. The blinking light is a system check that self resolves after a few moments.
  2. Gas supply issue: If the furnace is experiencing gas supply issues, it will blink severally depending on the nature of the problem. Common supply issues are supplier challenges, low pressure, gas blockage, and a malfunctioned gas valve.
  3. Ignition failure: You might have run into this problem a couple of times if you’ve used gas furnaces for an extended period. Ignition failure occurs when you try to light the furnace, but nothing happens. It can point to many underlying issues, such as a defective pilot system, dirty orifices, and the absence of gas.
  4. Issues with the safety switches: The average furnace has at least three different safety switches, including the flame rollout switch, pressure limit switch, and fan limit switch. Whenever one of the switches malfunctions, the furnace will blink severally, depending on the specific issue, to alert you.
  5. Furnace lockout: Finally, a furnace will also blink several times if the unit is in a lockout. Lockout is a non-responsive state in which the furnace ignores most inputs. It usually happens when you attempt to restart the furnace too many times after a previous issue, such as a safety switch failure.

Typical Furnace Error Codes

As you can tell from the above discussion, the biggest issue with the flashing furnace light is that it can mean anything literally. It could be a gas supply issue, a pilot light issue, an electrical power issue, or even a matter that requires safety cutoff. 

To this end, the first thing you need to do when the furnace begins to blink is to get close and observe the flashing light. Specifically, you need to count the number of times it blinks before breaking. Usually, it will blink x-times times, break, then blink again x-times – in a loop. 

If you can count the number of times it blinks between breaks, you’re halfway to solving the underlying issue. 

The “number of times” the flashing light blinks is known as an “error code” as it hints at the underlying issues. The following are typical codes and what they mean;

  1. Two (2) flashes: Mean the furnace is likely blowing cold air because it’s dropping the flame, i.e., the flame is feeble.
  2. Three (3) flashes: Indicate a problem with the pressure switch. Perhaps the pressure switch is open, making it impossible to run the furnace. Maybe it’s stuck. 
  3. Four (4) flashes: Indicate an issue with the limit switch. Could the limit switch be tripped? If so, perhaps you had a flame rollout or a moment of overheating.  
  4. Six (6) flashes: Are a sign that the furnace has a problem with polarity or grounding. This is an important electrical issue that can compromise the furnace’s circuitry. 
  5. Seven (7) flashes: Are a sign that you have a problem with the gate valve, the “gate” that controls the flow of gas into the furnace. Is it blocked? 
  6. Nine (9) flashes: Are a sign of ignition issues. Your furnace cannot ignite for one reason or the other. You need further tests to pinpoint the problem. 

If the flashing light goes on 22 times, then the flame itself has an issue. Maybe it’s too weak or burning unhealthily. 

Reasons the Light on Your Furnace is Blinking

The light on your furnace blinks for two main reasons. First, it blinks to alert you of an ongoing issue within the furnace. This way, you can take proper steps to stay safe and get the issue resolved. 

Secondly, the lighting is also present to help you confirm when the issue is ultimately resolved. The problem isn’t solved until the blinking light is gone. 

What to Do if the Furnace Light is Blinking

You need to do two things when your furnace begins to blink. First, make sure you and everyone else within the home are safe. This is critical as sometimes the blinking LED lights can be accompanied by gas leaks. Make sure everyone is safe,

Next, take appropriate steps to fix the underlying issue. Read the error code, cross-check with your owner’s manual to find out what it means, and take necessary action. This may mean restarting the furnace, repairing a few sections, or replacing a few parts. 

How to Restart Your Furnace Pilot Light

If all you need to do to fix the issue is to restart the issue, you’re in luck. Restarting the furnace means re-booting the system so that it self-resolves the ongoing problem. 

  1. Turn off the furnace 
  2. Shut down power at the breaker
  3. Turn off the gas supply
  4. Change the filter 
  5. Troubleshoot the pilot light
  6. Turn back gas supply and then electric power
  7. Switch the furnace back ON

When is a Blinking Furnace Light Dangerous?

The blinking furnace light by itself isn’t dangerous. Unfortunately, sometimes the light might be accompanied by unwanted incidents that make the situation unsafe. You need to take extra caution if you notice the following; 

  • A strong smell of gas (rotten egg)
  • The carbon monoxide sensor beeping
  • Overheating within your rooms

That’s all you need to know about blinking red lights on the furnace. Don’t hesitate to contact your HVAC technician if the issue persists even after restarting the furnace.