Trane and American Standard furnace flash codes

Trane's integrated furnace control reports faults as a flash count, and uses the flash rate itself to signal normal operation — slow for idle, fast for a call for heat.

Also covers: American Standard — same manufacturer, same controls, same codes.

Trane and American Standard are the same manufacturer and use the same integrated furnace control. Unlike most manufacturers, Trane uses the rate of flashing as well as the count: a slow steady flash means idle with no call for heat, and a fast steady flash means the furnace is responding to a call. Neither is a fault. Counted flashes from two to nine are the actual fault codes.

Worth knowing before you count

Fast flashing means normal operation on a Trane control and means a fault on several other manufacturers' boards. If you have owned a different furnace before, that convention does not carry over. A steadily lit LED that never flashes is Trane's instruction to replace the control.

How Trane furnaces signal codes

Trane runs two diagnostic systems side by side, and they share no numbering at all. The flash-code system is a single LED counting out faults from two to nine, with the flash rate itself carrying the normal-operation states. The seven-segment system, used on two-stage variable speed furnaces such as the S9V2, shows alphanumeric codes like E2.1 and E3.2 on a small display with Menu and Option buttons beside it — and the display shows something at all times, including IdL for idle and Xt1 for first stage heat, so characters on the screen are not automatically a fault. The tell is simple: if you are counting blinks you are on the flash-code system, and if you are reading characters you are on the seven-segment system. The seven-segment control also stores the last six faults in a menu, which means an intermittent fault that cleared itself is still recoverable — worth knowing before anyone holds the Option button for five seconds, which erases that list.

The Trane codes people look up most

On the flash-code side: 4 flashes is an open high limit, which is an airflow question — a clogged filter more often than a bad switch; 3 flashes is a draft pressure error pointing at the inducer and venting; 2 flashes is the lockout that follows too many failed ignition attempts; 8 flashes is a low flame sense signal, classic dirty-flame-sensor territory; and 9 flashes is an igniter circuit problem. Each has a seven-segment sibling — E04, E3.2, E2.1, E08 and E6.3 respectively — that describes the same physical fault on the other control, which is useful when a code was reported second-hand as a bare number.

Which Trane furnaces these pages cover

The flash codes are documented from Trane Installer's Guide 18-CD29D1-14-EN, Table 21, which covers the integrated furnace control used on Trane's flash-code furnaces. The seven-segment codes come from Installer's Guide 18-CE01D1-1E-EN for the S9V2 two-stage condensing variable speed furnaces. American Standard is the same manufacturer using the same controls, so both tables apply to equivalent American Standard models. If a code will not resolve against one table, check which system the furnace actually has before assuming the code is wrong.

What the common Trane fixes cost

The 8-flash and E08 low flame signal usually ends at flame sensor cleaning, $80–200 — the classic ten-minute fix. The 9-flash and E6.3 igniter faults run $150–350 installed, with the part $20–60 universal. Pressure switch codes (3 flashes, E3.2, E3.4) are $150–400 with the flue checked first; an open limit (4 flashes, E04) is $150–350 plus finding the airflow problem that tripped it. A continuously lit LED or E01 points at the control itself — $400–900 installed, though E12's open fuse is the $5–150 repair that impersonates a dead board. Blower communication faults E17 and E18 land in ECM territory: $700–1,200, or $900–1,500+ for variable-speed.

Trane and American Standard

2 flashes — System lockout — retries or recycles exceeded
3 flashes — Draft pressure error
4 flashes — Open high limit device
5 flashes — Flame sensed when no flame should be present
6 flashes — 115 volt AC power reversed, or poor grounding
7 flashes — Gas valve circuit error
8 flashes — Low flame sense signal
9 flashes — Ignitor circuit problem, or low voltage between neutral and 24 volt common
Continuous off — Check power
Continuous on — Replace the integrated furnace control
Flashing fast — Normal — call for heat
Flashing slow — Normal — no call for heat

Trane and American Standard seven-segment codes

E01 — Internal control failure
E2.1 — Retry exceeded — flame never sensed, one hour lockout
E2.2 — Recycles exceeded — flame sensed then lost, one hour lockout
E2.3 — First stage gas valve not energised when it should be, ten times
E3.2 — Open pressure switch, first stage
E3.4 — Open pressure switch, second stage
E3.1 — Shorted pressure switch, first stage
E3.3 — Shorted pressure switch, second stage
E04 — Open limit — thermal, rollout, or reverse airflow switch
E05 — Flame detected when it should not be present
E6.1 — Line voltage polarity reversed
E6.2 — Bad grounding
E6.3 — Igniter relay failed, or igniter open
E7.1 — First stage gas valve energised when it should be off
E08 — Flame current low but still usable
E09 — Open inducer limit switch or condensate pressure switch
E11 — Gas valve relay faults — five conditions in one code
E12 — Open fuse
E17 — Blower motor not responding to communication
E18 — Blower communication failure on the control
IdL, Xt1, Xt2, aRF and the other status codes — Normal operation — the display is not showing a fault
Which Trane code system you have — Trane furnaces use either flash codes or a seven-segment display, and they share no numbering

Other manufacturers

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.