Furnace troubleshooting

Top Lennox® Furnace Error Codes (and What They Mean)

While your Lennox® heating system cannot talk to you, it does have a process to tell you about a furnace error.

Its motherboard has double LED lights that can display a fault code. Based on the fault, your heating system could use continuous or flashing lights.

While there are a few basic furnace fixes you can do yourself, most repairs are best taken care of by experts. When your heater refuses to kick on or provide heated air, contact B & B Heating & Cooling at 314-325-7552 for experienced furnace repair in Florissant.

Our experts will rapidly spot and repair the issue, even if you don’t use a Lennox heater. We can repair whichever brands or models—and get the warmth restored to your home fast.


What Does the Flashing Light on My Heater Mean?

Your heater uses lights to flash code when it isn’t working right. It also works these lights to relay it’s heating like it should.

Normal operation involves:

  • Concurrent slow flash—furnace operating correctly.
  • Both lights flash fast—furnace is starting to call for heat.

If you see a lone light flashing slowly and the other flashing rapidly, your furnace might be experiencing a low flame signal. This can take place even when your furnace is operating like it should. It means the flame sensing rod may be dirty or in the bad location on the burner. Reach out to us at 314-325-7552 for assistance.

Here are some of the most common errors for Lennox furnaces.

Heater Will Not Start

Here are a few of the light sequences you might observe when your furnace refuses to or stay on. The majority of these errors must be taken care of by a technician, such as one from B & B Heating & Cooling.

  1. The pair of LED lights are extinguished. This indicates your furnace might not have electricity. Examine the breaker box to confirm the furnace fuse is not flipped. You should reset the fuse if it is in the “off” spot. If it immediately trips after you reset it, don’t touch the breaker and call us at 314-325-7552.
  2. A single light is unchanging and the other is flashing slowly. This signifies the flame rollout switch is likely open. The component is a critical safety tool that helps in preventing fires and carbon monoxide. You shouldn’t seek to handle this malfunction yourself.
  3. A single light is blinking fast and the other is flashing slowly. This typically signifies power polarity has been inverted. Your heater might have a wiring error that needs expert help from B & B Heating & Cooling.
  4. The pair of lights are blinking slowly. This signifies your heater’s blower motor possibly isn’t working. This component moves warm air from the HVAC system into your house. We can help in determining what’s causing an issue with this piece.
  5. An individual light is blinking slowly and the other is flashing rapidly. This signifies your HVAC system could have insufficient voltage or a short circuit. Contact our specialists at 314-325-7552 for support.
  6. One light is blinking on, on and off while the other flickers on, off, on. This means there could be a malfunction with your furnace’s control board or wiring. B & B Heating & Cooling can locate the issue and repair it.
  7. The duo of lights display alternate slow blinks. This indicates your HVAC system likely has a flame failure. There may be an issue with its gas supply, gas valve or ignitor control. Reach out to us at 314-325-7552 for assistance.
  8. An individual light blinks slowly while the other is steady. This typically signifies your furnace’s limit switch is malfunctioning. The switch stops your furnace from getting too hot. Get in touch with the experts at B & B Heating & Cooling for help.

Furnace Blower Runs But No Warm Air

Here’s what could be broken when you hear your heating system’s blower fan working, but you aren’t receiving any heat.

  • The duo of lights are giving every other rapid flickers. This indicates your furnace ignitor may not be working. This part ignites energy in your heating system to produce warmth and should be repaired by a technician from B & B Heating & Cooling.

Turn to Us for Expert Furnace Repair

When you need to have your HVAC equipment in working order quickly, turn to the technicians at B & B Heating & Cooling. Our techs will fix the error quickly and have your home feeling comfortable again in a short time. Reach out to us at 314-325-7552 or contact us online to request an appointment now.

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