HVAC Code Lookup

Lennox Furnace Code 7

Soft lockoutShown as: 7 rapid flashes (1/2 second on, 1/2 second off), then the LED stays off for 3 seconds and repeats

The primary or secondary limit switch is open, meaning the furnace got too hot. If the limit stays open longer than three minutes the control goes into Watchguard mode.

Manual wording: “7 - Primary or Secondary Limit Open or Watchguard Mode - Limit Switch Open longer than 3 minutes”

Documented for: ML180UHE, ML193UHE and other Lennox furnaces using SureLight integrated control 103217-03 or 107163-01

Likely causes, most common first

  1. Dirty air filter restricting airflow across the heat exchanger
  2. Closed, blocked or undersized supply and return registers
  3. Blower not moving enough air, or a failed blower motor
  4. Restricted or collapsed return duct

What you can safely check yourself

  • Check the air filter and replace it if it is dirty
  • Make sure supply and return registers throughout the house are open and not blocked by furniture or rugs
  • Check that the return grille is not covered
  • Turn the furnace power switch off for 30 seconds and back on once after the furnace has cooled

When to call a technician

If the code comes back after a clean filter and open vents, the limit is tripping for a real reason. Never jumper or bypass a limit switch. Have a technician check airflow, blower operation and firing rate.

A Lennox furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Sources

Other Lennox codes