HVAC Code Lookup

York Furnace 4 Red Flashes

Soft lockoutShown as: Four red flashes, then a two-second pause, repeating

The main limit switch has opened its normally closed contacts - the furnace is overheating. The control runs the blower and inducer while the limit is open to cool the heat exchanger down.

Manual wording: “4 RED FLASHES: This indicates that the main limit switch has opened its normally closed contacts. The control will operate the supply air blower and inducer while the open limit condition exists. Check for a dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate, loose limit switch wiring or faulty blower motor.”

Documented for: TG8S, TG9S, TM9E, TM9X, TM8X, TM9T, TM8T, TM9V, TM8Y, TM9Y

Likely causes, most common first

  1. Dirty air filter
  2. Improperly sized duct system
  3. Incorrect blower speed setting
  4. Incorrect firing rate
  5. Loose limit switch wiring
  6. Faulty blower motor

What you can safely check yourself

  • Check and replace the air filter - this is the number one cause
  • Open all supply registers and make sure return grilles are not blocked by furniture or rugs
  • Check that the furnace door panel is fully seated

When to call a technician

If the code comes back after a clean filter and open vents, the airflow problem is in the ductwork, blower or firing rate and needs a technician. Never jumper or reset the limit switch to keep the furnace running.

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

Sources

Other York codes