York 4 Flashes

What does York 4 Flashes mean?

Four flashes is a failed-ignition lockout: a flame signal of 0.2 microamps or greater could not be established in three consecutive attempts at the start of the heating cycle. After the third trial the gas valve relay opens, the inducer runs a five-second post-purge, and operation is inhibited. The lockout resets by cycling first-stage heat, cycling 24 VAC power, or after the 60-minute watchdog timer expires.

Symptoms

• Furnace tries to light several times then stops
• No heat; burners fail to stay lit
• ICB flashes a counted burst of 4 on the LED
• Auto-reset attempt occurs roughly an hour later

Common causes

• Insufficient or interrupted gas supply or improper manifold pressure
• Weak or misaligned ignitor or flame sensor (≈1/8" gap required)
• Poor electrical grounding of the control or cabinet
• Dirty or blocked burners restricting gas flow
• Wind, rain, or snow entering the heat compartment

Diagnostic steps

1. 01

   Verify gas supply and pressure

   Confirm the gas lines are purged of air, gas inlet pressure is correct, and the gas valve opens and provides proper manifold pressure.

2. 02

   Check the ignitor and flame sensor

   Verify the ignitor sparks with an approximate 1/8-inch gap to the crossover area of the left burner and the flame sensor is intact with an approximate 1/8-inch gap to the right burner.

3. 03

   Confirm grounding

   Verify proper electrical grounding and that the 24 VAC common and control cabinet ground references are intact, since poor ground prevents flame sensing.

4. 04

   Inspect the burners

   Confirm the burners are clean and free of blockages that could interfere with gas flow.

5. 05

   Protect against weather

   Verify there is no wind, rain, or snow entering the heat compartment and no air leaks or heat-exchanger breaches interfering with ignition.

When to call a professional

If the furnace still will not light after confirming gas supply and inspecting the ignitor and sensor, call a licensed HVAC technician. Diagnosing flame-sensing current, manifold pressure, and grounding requires a micro-amp meter and a manometer. Repeated ignition lockouts can also indicate a gas valve, control, or venting problem, and any suspected gas-supply or heat-exchanger issue must be evaluated professionally before the unit returns to service.