HVAC Code Lookup

York Furnace: 9 Flashes

A York furnace LED pattern starting with 9 flashes matches 2 documented codes: 9 red flashes, 9 red flashes (YP9C modulating). Watch the full pattern (short vs. long flashes) to tell them apart — all 2 are explained below.

Code 9 red flashes: Reversed line voltage polarity, a grounding problem, or reversed low voltage transformer wires

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

Full page for York code 9 red flashes

Code 9 red flashes (YP9C modulating): Reversed line polarity or improper grounding at the furnace

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

Reversed line polarity or improper grounding at the furnace.

Manual wording: “Nine Red Flashes - Reversed line polarity or improper grounding. Check polarity of the incoming power to the furnace. Check the grounding of the furnace, including the transformer ground and the L1 and neutral connections.”

Documented for: YP9C, YPLC modulating furnaces

Likely causes, most common first

  1. Line voltage hot and neutral reversed
  2. Poor or missing furnace ground
  3. Bad transformer ground or L1/neutral connection

What you can safely check yourself

  • If this appeared right after electrical work, mention that to the technician
  • Check the furnace breaker is fully on

When to call a technician

Polarity and grounding are line-voltage electrical work. Have a technician or electrician correct it.

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 9 red flashes (YP9C modulating)

Other York codes