Trane and American Standard E04 Error Code: Open limit
Updated October 2026 · Sourced from Trane and American Standard documentation
🧭 Check a few things first
An open limit: main thermal limit, rollout switch or reverse airflow switch.
Is it safe to keep running? Check the steps below first. Call a licensed HVAC technician. A tripped rollout or limit must be diagnosed by a professional, and safety switches must never be bypassed.
E04 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| E04 Shown on the 7-segment display of the integrated furnace control | Open limit | Trane S8B1 and S8X1 (single stage) and S8X2 (two stage) gas furnaces |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Replace a dirty air filter, then restore power and see if the code returns.
- Make sure supply and return vents are open and not blocked by furniture or rugs.
- Turn the furnace power switch or breaker off for 30 seconds, then back on, and see if the code clears.
🛑 Stop and call a licensed pro if
- Call a licensed HVAC technician. A tripped rollout or limit must be diagnosed by a professional, and safety switches must never be bypassed.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Flame rollout, limit or pressure switch codes that come back after one reset.
- Anything involving the control board, gas valve, flame sensor, igniter or venting.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Trane and American Standard code
- Count the LED flashes through the blower door window before you switch anything off. Cutting power can clear the code.
- Replace or clean the furnace air filter.
- Check the thermostat: correct mode, set above room temperature, and fresh batteries.
- Make sure the furnace power switch and breaker are on. If the furnace has locked out, turning the power off and back on once restarts it.
- Make sure the gas valve is in the ON position, following the lighting instructions on the furnace label only.
- On high-efficiency furnaces, look at the outside vent and intake pipes for snow, ice, leaves or nests (look only, do not take pipes apart).
Source: Trane Installer's Guide 18-CE14D1-1A-EN (04/2020), Integrated Furnace Control Display Codes, p.58. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Shaun Cain · Certified HVAC & Refrigeration Technician · Ask an HVAC technician
Related Trane and American Standard codes
E2.1 : Retry exceeded (flame never sensed)E2.2 : Recycles exceeded (flame lost)E3.1 : Shorted pressure switch, 1st stageE3.2 : Open pressure switch, 1st stageE3.4 : Open pressure switch, 2nd stageE05 : Flame detected, should not be presentE6.1 : Voltage reversed polarityE6.2 : Bad groundingE6.3 : Igniter relay fails or igniter openE08 : Low flame currentE12 : Open fuse2 flashes : System lockout, retries or recycles exceeded