Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
York Furnace Error Codes — Quick Reference
York furnaces flash a diagnostic LED on the control board inside the lower access panel. Count the repeating blink sequence. York (owned by Johnson Controls) shares control board platforms with Coleman, Luxaire, and Champion — codes are the same across these brands. Two-stage and modulating York furnaces may display two-digit fault codes.
| Code | Meaning | Quick Fix |
|---|---|---|
| 1 flash | System lockout | Reset power; check igniter and gas |
| 2 flashes | Pressure switch stuck open | Check inducer, hose, drain |
| 3 flashes | Pressure switch stuck closed | Check pressure switch hose |
| 4 flashes | Open limit device | Replace filter; check blower |
| 5 flashes | Flame sense without call | Gas valve leak; call pro |
| 6 flashes | Reversed polarity | Fix line voltage wiring |
| 7 flashes | Gas valve energized — no call | Board or gas valve fault |
| 8 flashes | Low flame signal | Clean flame sensor |
| E2 | Ignition fault (some models) | Check gas valve, igniter |
| E3 | Pressure switch fault (some models) | Check inducer and hose |
| E4 | Limit fault (some models) | Filter, blower, airflow |
Technician Tips
Modern furnaces use LED flash codes on the control board to diagnose failures. Before calling for service, count the number of flashes between pauses and check your owner’s manual for the code chart. The most common furnace error — 1-4 flashes usually means ignition failure — is often caused by a dirty flame sensor. The flame sensor is a $15-30 part that takes 10 minutes to clean. Remove it with a 1/4” nut driver, gently scrub the metal rod with emery cloth or a dollar bill (yes, a dollar bill — it’s the right abrasiveness), and reinstall. This fixes about 60% of “no heat” service calls.
DIY vs Pro: Error codes related to pressure switches (usually 2-3 flashes) often indicate blocked vents or condensate drains — safe to check yourself. Codes related to gas valves or ignition modules (4+ flashes) are best left to a licensed HVAC technician.
Need Replacement Parts?
Before ordering, match the furnace part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
Most Common Codes
2 Flashes: Pressure Switch Stuck Open
York high-efficiency furnaces (90%+ AFUE, including the YP9C and TM9E models) frequently develop this fault from a blocked condensate trap. The condensate trap is a U-shaped assembly near the bottom of the furnace. Clear the trap of algae or sludge, pour water through to verify flow, and check the rubber hose connecting the trap to the pressure switch for kinks or cracks.
4 Flashes: Limit Device Open
A limit switch opened because heat exchanger temperature exceeded its setpoint. Start with the filter — York recommends checking it monthly. On York two-stage furnaces, also check that the gas valve is staging correctly; if the valve is firing at high stage when low stage is commanded, excess heat can trip the limit.
6 Flashes: Reversed Polarity
York control boards are polarity-sensitive. The hot (black) wire must be on the hot terminal, not neutral. This is wired at the furnace disconnect or the dedicated circuit breaker. Use a non-contact voltage tester to identify which wire is hot at the outlet, then verify the furnace is wired accordingly.
8 Flashes: Low Flame Signal
The flame sensor microamp reading is too low for reliable proving. York furnaces use a standard 4-inch flame sensor rod in the leftmost or second burner. Clean the rod with fine abrasive and reinstall. Check the ceramic insulator on the sensor for cracks — a cracked insulator causes current leakage that lowers the signal.
E2: Ignition Fault
On York furnaces equipped with alphanumeric display boards (YP9C series), E2 indicates ignition sequence failure. Inspect the hot-surface igniter visually — even a hairline crack causes failure. Measure resistance: 40–80 ohms is normal for silicon nitride igniters used in York furnaces.
E4: Limit Fault
Similar to 4 flashes but on newer control boards. Check duct static pressure if you have a manometer — York recommends a total external static pressure below 0.5” WC on most residential models.
When to Call a Pro
If the 5-flash (flame without call) or 7-flash (gas valve fault) code appears, turn off the gas supply to the furnace and call a licensed HVAC technician. These codes can indicate a gas valve that won’t close fully — a fire and CO hazard.