OEM Control Family: Trane CNT03076 / CNT05165 / White-Rodgers 50A65 • 80V Silicon Nitride HSI
Trane & American Standard Furnace Blink Codes Decoder (2, 3, 4 & 9 Flashes)
⚡ Instant OEM Answer (Trane / American Standard Red LED Codes):
Trane and American Standard furnaces flash Slowly (1 Hz) in normal standby and Rapidly during an active heat call. 2 Flashes means 1-hour Ignition Lockout (
SEN01114 sensor below 1.0 µA DC); 3 Flashes means Pressure Switch / split red silicone hose fault; 4 Flashes means Open High Limit; and 9 Flashes means an open 80V Silicon Nitride Igniter (IGN00145 outside 11–20 Ω).
CNT & 50A65 Integrated Furnace Control Matrix
Complete Trane & American Standard Diagnostic Flash Chart
Covers Trane XR80, XV80, XC80, XR90, XV95, TUH1, TDD1, TUD2, and American Standard Freedom 80/90/95 furnaces using CNT03076, CNT03797, CNT05165, and White-Rodgers 50A65-475 / 50M56D-751 boards. (Newer S8X1, S8X2, and S9V2 models display 3-character codes like E2_1 Lockout, E3_1 Pressure Switch, E4_1 High Limit.)
| Red Status LED | S8 / S9 7-Seg | Trane / AmStd OEM Meaning | OEM Part SKU & Triage Fix |
|---|---|---|---|
| Slow Flash (1 Hz) | IdL | Normal Idle Standby (Fast = Calling) | Zero faults. Note: Steady Solid ON on 50A65 = Internal Board Failure. |
| 2 Flashes | E2_1 / E2_2 | System Lockout (No Flame After 3 Retries) | Polish SEN01114 Flame Rod (1.8–6.0 µA DC) or test 80V IGN00145 Igniter. |
| 3 Flashes | E3_1 / E3_2 | Pressure Switch Error (Open or Closed) | Trim cracked tip off red silicone hose on inducer barb; flush condensate trap. |
| 4 Flashes | E4_1 / E4_3 | Open High Limit or Rollout Switch | Swap clogged air filter; check auxiliary button-reset limit on horizontal blower scroll. |
| 5 Flashes | E5_1 | Flame Sensed With Gas Valve Off | Inspect 24V gas valve shutoff seat and dry moisture off flame sense board spade. |
| 6 Flashes | E6_1 | 115V Line Polarity Reversed / Bad Ground | Verify 120V Hot/Neutral polarity or plug $14 bonding plug into portable generator. |
| 7 / 8 Flashes | E7_1 / E8_1 | Gas Valve Circuit Error / Low Flame Sense | 7 = Gas valve relay fault; 8 = Weak flame current (< 1.5 µA DC), clean sensor rod. |
| 9 Flashes | E9_1 / E9_2 | Open Igniter Circuit Detected Pre-Purge | Swap failed IGN00145 / IGN00152 Silicon Nitride Igniter (11–20 Ω cold at 70°F). |
⚠️ Critical Trane 80-Volt Igniter Mistake to Avoid:
Most Trane
50A65 and CNT03076 boards use step-down pulse-width modulation to send 80 Volts AC (not 120 Volts!) to an IGN00145 / IGN00152 Silicon Nitride igniter. If you install a generic 120V universal Silicon Carbide igniter without upgrading to a 120V-conversion kit (50M56D-751), the 120V igniter will glow dim cherry-red at 80V and never reach the 1,800°F methane ignition threshold!