HVAC Code Lookup

American Standard Furnace: 4 Flashes

Code 4 Flashes: Open temperature limit circuit

Soft lockoutShown as: 4 flashes, pause, repeat

Open temperature limit circuit. 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 Temperature Limit Circuit”

Documented for: *UD1 / *DD1 and CUB1 / CDB1 fan-assisted gas furnaces with the LED-only integrated furnace control

Likely causes, most common first

  1. Open temperature limit circuit
  2. Restricted airflow across the heat exchanger - the manual's own limit checkout deliberately trips the limit by restricting the airflow at the return
  3. Flame roll-out device tripped: all models have a thermal control device on the burner cover and 'in case of flame roll-out, the device will cause the circuit to open which shuts off all flow of gas'

What you can safely check yourself

  • Change your filter - a dirty filter can cause your furnace to stop working
  • Check that supply registers and return grilles are open and unblocked
  • Make sure the furnace door is on properly after changing the filter, as this can prevent the furnace from starting
  • Look for snow, ice, weeds, or grass blocking the furnace venting

When to call a technician

If the code returns after a clean filter and open vents, call a technician. A tripped flame roll-out device in particular means combustion gas escaped the burner box and must be diagnosed before the furnace is run again. Never reset or bypass a limit or roll-out switch yourself.

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

Sources

Full page for American Standard code 4 Flashes

Other American Standard codes