HVAC Code Lookup

York Furnace 3 Red Flashes

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

Other York codes