What Does A Blinking Green Light On A Furnace Mean?

A blinking furnace is never good news. Although some furnaces blink even when in perfect shape, the flashing LED is often a sign of trouble. 

Indeed, if your furnace is blinking but still running, you should count yourself lucky. Sometimes it will blink and then go off right after. It may even refuse to come back on, indicating the unit is in “lockout” mode. 

We want to focus on instances when the furnace is blinking green. What does the green flashing light mean, when should you be worried, and what can you do about the blinking furnace? Let’s begin with a simple question;

Should My Furnace Light Be Blinking?

Should it be blinking? Should it be lighting bot not blinking? Or, should the light be off in the first place?

The answer depends on the type of furnace. However, generally, the furnace will blink even when running perfectly. 

If your furnace is in excellent working condition, currently switched ON, and working usually, it will blink green – but fast. It’s the ultimate sign that the furnace is generating enough heat to keep your home warming and hasn’t encountered any issues so far. 

In such furnaces, if the furnace is not lighting at all (no green, red, or yellow LED lighting), it’s a sign that the unit is OFF. Alternatively, It may mean that the furnace is switched ON but not getting any electric power to the board. Perhaps a plug or wire within the furnace is loose, or maybe the breaker circuit is tripped. 

However, if a green light is ON but continuous (no blinking), it’s usually a sign that the IFC circuit board is defective and needs replacing. 

Reasons the Light on your Furnace is Blinking

The flashing light on your furnace could point to many different issues. It depends on the color of the flashing light, the number of times it flashes, and the type of furnace. 

Generally, though, the gas furnace will blink if it encounters an issue in four primary areas, as follows;

A thermostat Problem

The blinking thermostat could point to a dead or malfunctioning thermostat. It can also indicate the poorly positioned or missing thermostat. For instance, if it signals that the thermostat is missing yet you remember inserting it back after the last DIY troubleshooting, the thermostat may not be held firmly in position. 

Ignition System Problem 

The blinking light can also signal trouble in the ignition process. Perhaps the pilot light is out. Or maybe it’s ON and working, but the burner system is compromised. Maybe the burner is dirty, or the orifices are blocked. In addition to the flashing lights, ignition issues may also cause the furnace to fail to light. 

Gas/Fuel Supply Issues 

 A flashing LED light on your furnace can also be a sign of problems in gas supply. Common supply issues include “no gas” incidents that may happen for various reasons, including supplier challenges, blocked gas lines, and a compromised gas valve. Alternatively, you may have gas but at low pressure. When this happens, the furnace will eventually flash severally to warn you. 

Power and Electrical Issues 

The furnace comprises many electrical components and several small circuits that together form the furnace circuitry. Therefore, the heating process may fail to the individual components, microcircuits, or the primary circuit. However, before it fails, the furnace may flash severally and send you relevant error codes to help you fix the problem. 

Compromised Safety Mechanism 

Finally, a blinking furnace light can also signal trouble in one of the numerous furnace safety mechanisms. For instance, the furnace employs a limit switch to guard against overheating and flame rollout. If the flame rolls out of the chamber into undesignated areas, the furnace may shut down and later flash severally to inform you why the shutdown was necessary. 

What Does a Green Flashing Light Mean on a Lennox Furnace?

The green flashing light on a Lennox flashing light means the same thing in most furnaces. It could be a sign of a healthy furnace or indicate a serious issue that requires immediate attention.

Refer above for the common causes. Additionally, check your owner’s manual to find out what the different flashes mean. If the manual doesn’t help, feel free to contact Lennox customer support. They’ll be glad to help.

Typical Furnace Error Codes

It’s impossible to enumerate all error codes from all furnace types. However, you may want to keep an eye out for the common codes. Note that all the codes below only apply if the furnace flashes green. 

  • Furnace flashes continually – and fast: This is what you want to see when heating your home. It’s a sign that the furnace is ON and doing its job well without any issues.
  • Furnace flashes continually – but slowly: This is a sign that the furnace is ON and in good working condition. However, the thermostat hasn’t requested heating.
  • Furnace flashes five times – between breaks: Here, the furnace flashes five times, takes a short break, then flashes five times again. It’s a sign that the flame is where it’s not supposed to be, i.e., the furnace has encountered a rollout.
  • Furnace flashes twice – between breaks: This is a sign that your furnace has entered lockout mode. While in a lockout, the furnace may become unresponsive to input until you reset it. In this case, the light will flash twice, take a break, then flash again twice.
  • When the furnace flashes seven times: If your furnace flashes seven times between breaks, it has gas valve issues. Perhaps the furnace has encountered a blockage, or the pressure is too low.
  • Eight flashes usually signal a low flame, while nine flashes signify a compromised ignition system.

Here is how to know if your furnace control board is bad

What to Do if Your Furnace Light is Blinking

What to do when the furnace light is blinking varies depending on the underlying issues. Nevertheless, you need to fix the issue. 

Sometimes turning the furnace off and then back on (i.e., resetting) can resolve the problem. However, you may often need to troubleshoot it manually and fix the issues either through repair or replacing the damaged part. 

How to Restart Your Furnace Pilot Light

If your furnace ran into an ignition problem, restarting the pilot light can resolve the issues. It’s a straightforward process;

  1. Locate the pilot light reset switch (consult the owner’s manual)
  2. Set the reset switch OFF
  3. Wait a minute or two
  4. Turn the knob to “Pilot”
  5. Use a lighter/match to light the pilot. Simultaneously, push in the reset button 
  6. Keep the reset switch pressed until the pilot light is burning steadily
  7. Release the button 
  8. Observe the pilot flame for a few moments to ensure it stays ON

When is a Blinking Furnace Light Dangerous?

Although the flashing pilot light is harmless in most cases, sometimes it can be dangerous. Specifically, you want to watch out for;

  • Gas smell around the heater
  • A beeping carbon monoxide sensor 
  • Overheating 

If you notice any of the above, shut down the furnace immediately and contact your HVAC technician. 

A flashing green light on your furnace isn’t always a good sign. Although it could be harmless, it may also point to a serious issue. So, it’s best to stop whatever you’re doing to troubleshoot and ideally fix the underlying issue before it’s too late.