HVAC Code Lookup

York Furnace: 3 Flashes

A York furnace LED pattern starting with 3 flashes matches 5 documented codes: 3 red flashes, 3 green flashes, 3 amber flashes (YP9C modulating), 3 red flashes (YP9C modulating), 3 green flashes (YP9C modulating). Watch the full pattern (short vs. long flashes) to tell them apart — all 5 are explained below.

Code 3 red flashes: The pressure switch contacts are open when they should be closed

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

The pressure switch contacts are open when they should be closed. The inducer is not producing enough draft to close the switch, so the control will not light the burners.

Manual wording: “3 RED FLASHES: This indicates the pressure switch contacts are open when they should be closed. Check for faulty inducer, blocked vent pipe, broken pressure switch hose, disconnected pressure switch or inducer wires or faulty pressure switch.”

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

Likely causes, most common first

  1. Faulty inducer (draft) motor
  2. Blocked vent pipe
  3. Broken pressure switch hose
  4. Disconnected pressure switch or inducer wires
  5. Faulty pressure switch

What you can safely check yourself

  • Go outside and check the vent and combustion air pipe terminations for snow, ice, leaves, insect nests or other blockage
  • Check the condensate drain and trap for a clog (on 90%+ furnaces a plugged drain can back up and open the pressure switch)
  • Replace a heavily clogged air filter

When to call a technician

If the outside pipes are clear and the code stays, a technician needs to test the inducer, hoses and switch. Do not jumper the pressure switch - it is what proves the furnace can vent safely.

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 3 red flashes

Code 3 green flashes: Confirmation that the stored error code memory has been cleared

StatusShown as: Three green flashes after holding the LAST ERROR button more than five seconds

Confirmation that the stored error code memory has been cleared. Not a fault.

Manual wording: “The LED will flash three green flashes when the memory has been cleared, then will resume the normal slow green flash after a five-second pause.”

Documented for: All UPG boards with a LAST ERROR button

Likely causes, most common first

  1. The LAST ERROR button was held for more than five seconds, clearing the fault history

When to call a technician

Not a fault. Clearing the fault history erases the evidence a technician uses to diagnose an intermittent problem, so leave the button alone before a service visit.

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 3 green flashes

Code 3 amber flashes (YP9C modulating): Normal operation - the burner is still on at the end of the heating cycle after the wall thermostat has been satisfied

StatusShown as: Three amber flashes, two-second pause, repeating

Normal operation - the burner is still on at the end of the heating cycle after the wall thermostat has been satisfied. Not a fault.

Manual wording: “Three Amber flashes - Normal operation, burner is on at end of heating cycle after wall thermostat has been satisfied.”

Documented for: YP9C, YPLC modulating furnaces

Likely causes, most common first

  1. Normal end-of-cycle burner operation on the modulating control

When to call a technician

No service needed.

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 3 amber flashes (YP9C modulating)

Code 3 red flashes (YP9C modulating): The pressure switch is open while inducer pressure is above the switch setpoint - the switch is open when it should be closed, so the burners cannot light

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

The pressure switch is open while inducer pressure is above the switch setpoint - the switch is open when it should be closed, so the burners cannot light.

Manual wording: “Three Red Flashes - Pressure switch open with inducer pressure above pressure switch setpoint (switch is open when it should be closed). Check pressure switch and pressure transducer.”

Documented for: YP9C, YPLC modulating furnaces

Likely causes, most common first

  1. Faulty pressure switch
  2. Faulty pressure transducer

What you can safely check yourself

  • Check the outside vent and intake pipe terminations for snow, ice, leaves or nests
  • Check the condensate drain and trap for a clog

When to call a technician

If the venting and drain are clear, the pressure switch or transducer needs a technician with a manometer.

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 3 red flashes (YP9C modulating)

Code 3 green flashes (YP9C modulating): Indicator for 'Error codes cleared from memory'

StatusShown as: Three green flashes after holding the LAST ERROR button more than five seconds

Indicator for 'Error codes cleared from memory'. Not a fault.

Manual wording: “Three Green Flashes - Indicator for "Error codes cleared from memory".”

Documented for: YP9C, YPLC modulating furnaces

Likely causes, most common first

  1. The stored fault history was cleared with the LAST ERROR button

When to call a technician

Not a fault, but clearing the history erases what a technician needs to chase an intermittent problem - leave it alone before a service visit.

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 3 green flashes (YP9C modulating)

Other York codes