Trane Furnace error codes
23 Trane furnace codes and problems, each with ranked causes, safe homeowner checks and honest repair costs. Count the flashes or read the code on your control board, then find it below. Legends vary by board revision, so confirm against the label inside your unit's door. American Standard uses the same control boards — see American Standard furnace codes.
Of these, 22 need a professional repair and 1 is usually safe to check yourself.
| Code | What it means | Severity |
|---|---|---|
| 2 flashes | Trane furnace flashing 2 means a system lockout from failed ignition retries. Learn causes, safe checks, and repair costs ($0 DIY - $1,200). | Call a pro |
| 3 flashes | Trane furnace 3 flashes means a pressure switch error. Learn causes like blocked vents, a bad inducer, and fixes plus repair costs. | Call a pro |
| 4 flashes | Trane furnace 4 flashes means an open temperature limit or rollout circuit. Causes, safe checks, fixes and repair costs for US homeowners. | Call a pro |
| 5 flashes | Trane furnace 5 flashes means flame detected with the gas valve off. Causes, safe checks, technician diagnosis and repair costs from $0 to $600. | Call a pro |
| 6 flashes | Trane furnace 6 flashes means reversed 115 VAC polarity or poor grounding. Causes, safe homeowner checks, and real US repair costs for this pro-only fix. | Call a pro |
| 7 flashes | Trane furnace 7 flashes means a gas valve circuit error. Learn the causes, safe checks, and repair costs — commonly $150–$1,200+ for a pro fix. | Call a pro |
| 8 flashes | Trane furnace 8 flashes means a low flame sense signal from a dirty flame sensor or weak flame. Causes, fixes and repair costs explained. | Call a pro |
| 9 flashes | Trane furnace 9 flashes means an open igniter circuit or no current draw. Causes, safe checks, and repair costs from $0 DIY to $250. | Call a pro |
| Code 90 (2 blinks) | Trane or American Standard furnace flashing code 90 / 2 blinks? What this inducer and pressure-switch fault family means, safe checks, and repair costs. | Call a pro |
| Blower not running | Trane furnace blower not running? Causes from door switches to bad capacitors or blower motors, DIY checks, and honest repair costs. | Call a pro |
| Blower won't shut off | Trane furnace blower runs constantly? Causes include thermostat fan settings, a stuck limit switch or bad control board, plus fixes and repair costs. | DIY-friendly |
| Blowing cold air | Trane furnace blowing cold air? Causes from thermostat fan settings to failed ignition, flame sensor & control board, plus fixes and honest US costs. | Call a pro |
| Clicking but not starting | Trane furnace clicking but not starting? Causes include a failing ignition relay, weak transformer, or draft inducer. Fixes and costs from $0 DIY to $600. | Call a pro |
| Flame sensor problems | Trane furnace flame sensor problems cause short cycling and lockouts. Causes, safe homeowner checks, how a technician diagnoses it, and real repair costs. | Call a pro |
| Ignition lockout | Trane furnace ignition lockout means failed ignition after repeated tries. Causes, safe checks, fixes and costs from $0 DIY to $700 pro. | Call a pro |
| Keeps shutting off | Why your Trane furnace keeps shutting off — overheating limits, flame loss, pressure switches and dirty flame sensors — plus fixes and costs from $0 to $3,500+. | Call a pro |
| Leaking water | Trane furnace leaking water is usually a clogged condensate drain, bad trap, or cracked inducer. See causes, safe checks, fixes & real US costs. | Call a pro |
| Loud bang on startup | Trane furnace makes a loud bang on startup from delayed ignition or duct flexing. Causes, safe checks, CO safety and repair costs ($0 DIY–$3,500+). | Call a pro |
| Pressure switch stuck open | Trane furnace pressure switch stuck open: causes from blocked vents to a failing inducer, safe checks, and repair costs from $0 DIY to $1,200. | Call a pro |
| Runs constantly but not enough heat | Trane furnace runs nonstop but can't keep up? Causes from dirty filters to failing heat exchangers, DIY checks, fixes and honest US repair costs. | Call a pro |
| Short cycling | Trane furnace short cycling? Causes include a dirty filter, overheating limit trips, flame-sensor and control-board faults, plus fixes and US repair costs. | Call a pro |
| Won't ignite | Trane furnace won't ignite? Common causes include a bad igniter, dirty flame sensor, or ignition lockout, plus DIY checks and repair costs. | Call a pro |
| Won't turn on | Trane furnace won't turn on? Causes from tripped breakers to failed transformers, blower door switches & control boards, plus fixes and honest US costs. | Call a pro |
Don't see your code? Look it up — every search we can't answer goes into the queue for the next guide.