American Standard S8X1 furnace code E04: Safety limit circuit open
Safety issue — act now
What does E04 mean on an American Standard Silver S8X1 gas furnace display? E04 means one of three safety switches is open: the main thermal limit, a flame rollout switch or the reverse-airflow switch. The code does not say which one tripped.
This condition involves the gas or combustion side. If you smell gas or a CO alarm sounds: leave, then call your gas utility. Diagnostic info here is reference — combustion repairs are for licensed technicians. All six emergency signs →
A technician must determine which switch opened and why. Rollout and limit trips need investigation of airflow, combustion and venting; the switches must never be bypassed or reset as a fix.
Possible causes
- Restricted airflow from a clogged filter or blocked registers TECH
- Flame rollout condition requiring combustion and venting investigation TECH
- Insufficient blower airflow through the furnace TECH
Parts for this code
No model-verified part number is listed here. Have the fault diagnosed and the correct part matched to your furnace before ordering.
Questions about this code
What does E04 mean on an American Standard Silver S8X1 gas furnace display?
E04 means one of three safety switches is open: the main thermal limit, a flame rollout switch or the reverse-airflow switch. The code does not say which one tripped.
How do I fix American Standard S8X1 furnace code E04?
If you smell gas or a CO alarm sounds, leave now without touching switches or the thermostat, and call the gas utility or 911 from outside. Otherwise set the thermostat to OFF, keep the furnace off and book service. Do not reset any rollout switch.
How much does it cost to fix American Standard S8X1 furnace code E04?
Cost depends on which switch tripped and why. A filter-related limit trip differs greatly from rollout or venting repairs, so diagnosis must come first.
Related symptoms
These symptoms can appear alongside this code. The link is an association, not a diagnosis, and code meanings vary by brand, model and control.
Applies to
S8X1A040M3PSCA · S8X1B040M2PSCA · S8X1B060M4PSCB · S8X1B080M4PSCB · S8X1C080M5PSCA · S8X1C100M5PSCB · S8X1D120M5PSCA
Different American Standard generations use different code maps. If your series isn't listed, don't assume this meaning — check your blower-door label.
Verified against Installation, Operation, and Maintenance — Upflow/Downflow/Horizontal Gas-Fired,1–Stage and2–Stage Induced Draft Furnaces with High Efficiency Motor, p.58
Verified against Installation, Operation, and Maintenance — Upflow/Downflow/Horizontal Gas-Fired,1–Stage and2–Stage Induced Draft Furnaces with High Efficiency Motor, p.69
Verified against Installer’s Guide — Upflow/Downflow/Horizontal Gas-Fired,1–Stage and2–Stage Induced Draft Furnaces with High Efficiency Motor, p.58
Last verified 2026-10-07 · page updated 2026-10-07 · how we verify
Related American Standard furnace codes
These codes use the same american standard silver s8x1 furnace control display (2024 iom) system.