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.

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
Flashing slow — Normal — no call for heat
Flashing fast — Normal — call for heat
Continuous on — Replace the integrated furnace control
Continuous off — Check power

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.