Heating # Trane gas furnace with the S9X1/S9X2/S9B1 IFC fault codes (S9X1, S9X2, S9B1, American Standard *UX1 / *UX2 equivalents) Every fault code for this Trane gas furnace with the S9X1/S9X2/S9B1 IFC is below, with what it indicates and a verdict: whether you can safely check it or it is a call for a technician. Here the code shows on a 7-segment display. The source is Trane's own service manual. Confirm your model is on the list; other Trane controls use different codes. **Before any code:** if you smell gas or a carbon monoxide alarm is sounding, this is not a diagnostic exercise. Leave the house and call from outside. [What to do about a gas smell or a CO alarm](https://hvacbuddy.shop/questions/noises-and-smells/). ## How to read the display These Trane furnaces show codes on a seven-segment display on the integrated furnace control (IFC). A fault is an "e" code such as e2.1 or e04. In normal operation the display instead reads IDL for idle, or a mode like Xt1 for first-stage heat, which is not a fault. The last six faults can be read back from the IFC's menu. American Standard furnaces use the same control and the same codes, but confirm your model against the label inside the furnace before relying on this list. ## What each code means Each code carries a safety verdict. **Caution** means there is a check you can safely make; **pro-only** means the correct repair is certified work and we do not walk through it here. ## [e2.1 — Retry exceeded — ignition lockout](#e2-1) Caution — power off first Retry exceeded — ignition lockout Flame was never sensed after three tries in one call for heat, so the furnace shut the gas off and locked out for one hour. It is the most common no-heat lockout on this control. **What you can do:** Confirm the gas is on and the filter is clean, then reset once. If it locks out again, the igniter, flame sensor or gas supply is a technician's diagnosis. ## [e2.2 — Recycles exceeded — flame kept dropping out](#e2-2) Caution — power off first Recycles exceeded — flame kept dropping out Flame was sensed but then lost, ten times in a row, and the furnace locked out for one hour. It usually points at a weak flame or a flame sensor that stops reading it partway through. **What you can do:** Check the filter and that the gas is fully on, then reset once. If it keeps dropping flame, it is a flame-sensing or combustion fault for a technician. ## [e3.2 — Open pressure switch, first stage](#e3-2) Caution — power off first Open pressure switch, first stage After the inducer started, the first-stage pressure switch never confirmed closed. Common causes are a blocked vent or intake, a blocked condensate drain, or a weak inducer. **What you can do:** Clear the outdoor intake and exhaust terminations of snow, leaves or a nest. The drain and the inducer are a technician's diagnosis. ## [e04 — Open limit — thermal, rollout, or reverse airflow](#e04) Caution — power off first Open limit — thermal, rollout, or reverse airflow A safety limit opened: the main thermal limit, a flame rollout switch, or a reverse-airflow switch. A plain thermal limit is usually restricted airflow, but a rollout is a combustion safety trip and is not the same thing. **What you can do:** Start with the filter — restricted airflow trips the thermal limit and it is the safe fix. But if the rollout switch is what opened, do not keep resetting it: that is a combustion fault a technician must find before the furnace runs again. ## [e05 — Flame detected when there should be none](#e05) Licensed professional required Flame detected when there should be none The control sensed flame when the gas valve should be closed. Because it can mean a gas valve that is not shutting off, it is not a wait-and-see code. **What you can do:** Call a technician. If you also smell gas, leave and treat it as the emergency at the top of this page. ## [e6.1 — Reversed line-voltage polarity](#e6-1) Licensed professional required Reversed line-voltage polarity Line and neutral are reversed, and the furnace will not run for heat until corrected. On a newly installed or serviced furnace this points back at the wiring. **What you can do:** Line-voltage wiring is for an electrician or the installer. ## [e6.2 — Bad grounding](#e6-2) Licensed professional required Bad grounding The control has detected an improper ground. Flame sensing depends on a good ground, so a grounding fault often shows alongside flame problems. **What you can do:** Grounding is line-voltage electrical work for a technician or electrician. ## [e6.3 — Igniter relay or open igniter](#e6-3) Licensed professional required Igniter relay or open igniter The control could not confirm a working igniter — either the igniter relay failed or the igniter circuit is open. **What you can do:** Igniters are fragile and this is a control and line-voltage diagnosis for a technician. ## [e7.1 — Gas valve energized when it should be off](#e7-1) Licensed professional required Gas valve energized when it should be off The first-stage gas valve is being powered when the control commanded it off. Anything where the gas valve does not match its command is prompt technician work. **What you can do:** Call a technician promptly. If you smell gas, leave and treat it as the emergency at the top of this page. ## [e08 — Low flame current](#e08) Licensed professional required Low flame current The flame is lit and the furnace keeps running, but the flame-sense current has fallen toward the lower limit. It usually means a dirty or aging flame sensor and is a warning before an e2.2 lockout. **What you can do:** Servicing the flame sensor is combustion-side work this site does not walk through. Booking it before it becomes a lockout saves a cold night. ## [e09 — Open inducer limit or condensate pressure switch](#e09) Caution — power off first Open inducer limit or condensate pressure switch The inducer limit switch or the condensate pressure switch is open. On a condensing furnace this frequently means the condensate drain is backing up. **What you can do:** If you can see the condensate drain line and it is obviously blocked or the collection area is full, that is worth noting for the technician — but clearing the drain and the switch itself is their job. ## [e11 — Gas valve relay fault](#e11) Licensed professional required Gas valve relay fault The control reports a gas valve relay that is stuck or a valve energized or de-energized when it should not be. Any mismatch between the gas valve and its command is a safety-relevant fault. **What you can do:** This is a gas-side control fault for a qualified technician. There is no homeowner action. ## [e12 — Open fuse](#e12) Licensed professional required Open fuse The control's low-voltage fuse is open, which almost always means a short somewhere in the 24-volt wiring rather than a bad fuse on its own. **What you can do:** Replacing the fuse without finding the short just blows the next one. Finding it is a technician's job. ## [e01 — Internal control failure](#e01) Licensed professional required Internal control failure The integrated furnace control has detected an internal fault of its own. The manual treats this as the control itself, reached after other causes are ruled out. **What you can do:** Replacing the control is a technician's job, and a good one confirms the other causes are ruled out first. ## A note on brand names We use the Trane name only to identify which equipment these codes apply to. We are not affiliated with Trane and are not an official support channel, and the code map above is written in our own words from the published service manual cited below. Sources (1) - Trane — [S9X1 / S9X2 / S9B1 Gas Furnace — Service Facts — Integrated Furnace Control Display Codes — Error Codes table (form S9XB-SF-1E-EN, p. 33)](https://assets.unilogcorp.com/267/ITEM/DOC/TRANE_S9X2D120U5PSBA_Service_Manual.pdf) (accessed 2026-08-22) By [HVACBuddy Editorial Team](https://hvacbuddy.shop/authors/editorial-team/). Last reviewed: 2026-08-21. HVACBuddy publishes independent information. We do not install or service equipment, we do not dispatch contractors, and we do not sell leads. Nothing here is engineering, tax, or legal advice.