HVAC Code Lookup

York Furnace 9 Red Flashes

Hard lockoutShown as: Nine red flashes, then a two-second pause, repeating

Reversed line voltage polarity, a grounding problem, or reversed low voltage transformer wires. The furnace will not start the ignition sequence until this is corrected, and both heating and cooling are affected.

Manual wording: “9 RED FLASHES: Indicates reversed line voltage polarity, grounding problem or reversed low voltage transformer wires. Both heating and cooling operations will be affected.”

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

Likely causes, most common first

  1. Reversed line voltage polarity (hot and neutral swapped) at the furnace or at the branch circuit
  2. Poor or missing furnace ground
  3. Reversed low voltage transformer wires
  4. Flame probe shorted to the chassis

What you can safely check yourself

  • If this appeared right after electrical work or a new outlet/breaker was installed, mention that to the technician
  • Check the furnace breaker is fully on

When to call a technician

Polarity and grounding faults are line-voltage electrical work. Have a technician or electrician check the polarity and ground at the furnace and at the branch circuit.

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

Sources

Other York codes