HVAC Code Lookup

Trane Furnace 4 Flashes

Soft lockoutShown as: 4 flashes, pause, repeat

Open high limit device. A temperature limit switch has opened because the furnace got too hot, which closes the gas valve and stops the burners.

Manual wording: “4 Flashes --- Open High Limit Device”

Documented for: *UH1 / *DH1 condensing furnaces (XR 95 family) and other Trane furnaces using the LED-only integrated furnace control

Likely causes, most common first

  1. Restricted airflow across the heat exchanger - the manual's own limit checkout deliberately trips the limit by 'blocking the return air', which is what a dirty filter or blocked returns do in service
  2. Blocked vent or combustion air inlet terminations (the manual's burner-box limit reset step says 'The vent and combustion air inlet terminations should be checked for blockage')
  3. Faulty limit switch

What you can safely check yourself

  • Check the air filter and clean or replace it if it is dirty
  • Check that supply registers and return grilles are open and not blocked by furniture or rugs
  • Check the outdoor vent and combustion air intake terminations for blockage

When to call a technician

If the code comes back after a clean filter and open vents, the furnace is overheating for a reason a technician must diagnose. The burner-box manual-reset limit 'must be reset by a qualified servicer' per the manual - do not press or bypass safety limits yourself.

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

Sources

Other Trane codes