HVAC Code Lookup

American Standard Furnace Code E04

Safety fault

A safety limit has opened: the main thermal limit, a flame rollout switch, or the reverse airflow switch. The furnace has stopped heating.

Manual wording: “Open Limit (Main Thermal, Rollout Switch, or Reverse Airflow Switch)”

Documented for: A951X condensing and A801X induced draft furnaces with the seven-segment IFC display

Likely causes, most common first

  1. Open limit (main thermal, rollout switch, or reverse airflow switch)
  2. Restricted airflow across the heat exchanger from a dirty filter or blocked returns
  3. Blocked venting
  4. Flame rollout, which indicates a blocked heat exchanger or burner problem

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
  • Look for snow, ice, weeds, or grass blocking the furnace venting
  • Make sure the furnace door is on properly after changing the filter

When to call a technician

If the code returns after a clean filter and open vents, call a technician. A tripped rollout switch means combustion gases came out of the burner box and must be diagnosed before the furnace runs again. Never reset or bypass a rollout or limit switch yourself.

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

Sources

Other American Standard codes