HVAC Code Lookup

York Furnace: 4 Flashes

A York furnace LED pattern starting with 4 flashes matches 4 documented codes: 4 red flashes, 4 amber flashes, 4 amber flashes (YP9C modulating), 4 red flashes (YP9C modulating). Watch the full pattern (short vs. long flashes) to tell them apart — all 4 are explained below.

Code 4 red flashes: The main limit switch has opened its normally closed contacts - the furnace is overheating

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

Full page for York code 4 red flashes

Code 4 amber flashes: The control is receiving a Y

WarningShown as: Four amber flashes, then a two-second pause, repeating

The control is receiving a Y (cooling) signal from the thermostat without a G (fan) signal. The furnace still heats and cools normally, but the wiring is wrong and the code is displayed to flag it.

Manual wording: “4 AMBER FLASHES: The control is receiving a "Y" signal from the thermostat without a "G" signal... Verify that the "G" wire from the thermostat is connected properly.”

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

Likely causes, most common first

  1. The G wire from the thermostat is not connected properly

What you can safely check yourself

  • If a new thermostat was recently installed, mention it to the technician - the G (fan) wire is most likely off or on the wrong terminal

When to call a technician

Thermostat wiring corrections are quick for a technician. Left alone, the indoor blower may not run correctly during cooling.

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

Sources

Full page for York code 4 amber flashes

Code 4 amber flashes (YP9C modulating): The furnace has automatically cut back its heating output because airflow through the house side is restricted

WarningShown as: Four amber flashes, two-second pause, repeating

The furnace has automatically cut back its heating output because airflow through the house side is restricted.

Manual wording: “Four Amber Flashes - Heating capacity is reduced due to restriction in the circulating air system. Check for dirty filter or closed registers.”

Documented for: YP9C, YPLC modulating furnaces

Likely causes, most common first

  1. Dirty air filter
  2. Closed or blocked supply registers

What you can safely check yourself

  • Check and replace the air filter
  • Open all supply registers and clear anything blocking the return grille

When to call a technician

If the code stays after a clean filter and open registers, the duct system or blower needs a technician.

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

Source

Full page for York code 4 amber flashes (YP9C modulating)

Code 4 red flashes (YP9C modulating): High limit switch open, defective temperature sensor, or the 24 volt fuse is open

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

High limit switch open, defective temperature sensor, or the 24 volt fuse is open. Usually an airflow restriction is making the furnace overheat.

Manual wording: “Four Red Flashes - High limit switch open or defective temperature sensor or 24 volt fuse is open. This may be caused by a dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow an open fuse on the control board.”

Documented for: YP9C, YPLC modulating furnaces

Likely causes, most common first

  1. Dirty air filter
  2. Improperly sized duct system
  3. Faulty blower motor
  4. Restricted circulating airflow
  5. Open fuse on the control board

What you can safely check yourself

  • Check and replace the air filter
  • Open all supply registers and clear the return grille
  • Check that the furnace door panel is fully seated

When to call a technician

If the code returns with a clean filter and open vents, have a technician check the blower, ductwork and the board fuse. Never bypass the limit switch.

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

Source

Full page for York code 4 red flashes (YP9C modulating)

Other York codes