HVAC Code Lookup

Trane 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: S8B1, S9V2 and S9V2-VS furnaces

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 vent or combustion air terminations
  4. Flame rollout, which indicates a blocked heat exchanger or burner problem

What you can safely check yourself

  • Check the air filter and clean or replace it if dirty
  • Check that supply registers and return grilles are open and unblocked
  • Check the outdoor intake and exhaust terminations for snow, ice, or debris

When to call a technician

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