Home Fault Codes

Lennox Furnace 5 Flashes: Meaning and Fix

Applies to: Lennox ML180UHE furnaces with integrated control 107163-01 (red LED flash codes).

5 Flashes
How 5 Flashes appears on a Lennox furnace display.

Also shown as: 5 flashes, five flashes

Reading the furnace display

A furnace reports faults on a small status LED on the control board, seen through the sight glass in the blower door, or on a two-digit display. Watch a full cycle of the pattern and count the flashes, including the pause between groups, before you decide what you saw. The code chart is on the label inside the blower door.

This page lists the fault codes this brand documents, with likely causes and a short repair path. The codes apply to model numbers such as ML180UHE; check the label on your unit to confirm yours.

What causes 5 Flashes

How to fix it

If you smell gas, leave the building and call your gas utility from outside; do not touch switches or the furnace. Switch the furnace power off before you open the blower door or touch the igniter or flame sensor, and call a licensed HVAC technician if you are not sure.

The code meaning comes from the manufacturer document listed under Sources. The causes and steps below are general troubleshooting guidance, not the manufacturer's service procedure.

  1. Check that the gas shut-off valve at the furnace is open. If you smell gas, leave the building and call your gas utility.
  2. The lockout clears by itself after one hour, or when power is cycled off and on.
  3. Switch the furnace power off before touching the flame sensor or igniter.
  4. If it returns, a technician should find why ignition keeps failing.
  5. Restore power and run a heating cycle. If the code returns, call a licensed HVAC technician and give them the code, the board label and the furnace model number.

Questions

What does 5 Flashes mean on a Lennox furnace?

On a Lennox ML180UHE control board (107163-01), 5 red LED flashes mean: watchguard: burner failed to light, exceeded maximum retries or recycles (1 hour lockout).

Can I reset the furnace myself?

The control can be reset by switching power off at the furnace switch or breaker for about 30 seconds, which clears some lockouts. If the same code returns, the fault is still present and the control will shut the furnace down again. Never bypass a safety switch to keep it running.

When should I call a technician?

Call a licensed HVAC technician for anything involving gas, the pressure switch, the limit or rollout switches, the igniter, the flame sensor or a control board replacement, or if the code keeps coming back after the simple checks.

Other brands with code 5 Flashes

The same code can mean something different on another maker's appliance. Check the brand before you act.

Chamberlain garage door openerNo RPM pulses detected in the first secondCraftsman garage door openerNo RPM pulses detected in the first secondGoodman furnaceOpen rollout switch or open fuse detectedLiftMaster garage door openerNo RPM pulses detected in the first secondTrane furnaceFlame sensed when no flame should be present

Other Lennox furnace codes

1 FlashReverse line voltage polarity or phasing of 120V power2 FlashesImproper earth ground3 FlashesBurner failed to light, or lost flame during heat demand4 FlashesLow flame signal, check flame sensor7 FlashesPrimary or secondary limit switch open, or Watchguard: limit open longer than 3 minutes8 FlashesRoll-out switch open

Sources

Part numbers are OEM references; confirm fit by your model number before ordering. Meanings compiled from manufacturer and parts-retailer documentation; see sources below. Unplug the appliance before opening it.

Applies to models including ML180UHE.