Inducer runs, ignitor glows, burners light briefly then go out; LED flashes three times repeatedly.

Safety first: Disconnect power before touching wiring or components.

• Verify correct tubing and wiring: Confirm the pressure switch tubing is connected to the correct port on the inducer housing and that the electrical connectors are firmly attached to the correct switch terminals.
• Check for stuck contacts: With power off, disconnect one wire from the pressure switch and measure continuity across the terminals. With no call for heat and inducer off, the switch should be open (no continuity). If it reads closed, the switch is stuck and should be replaced.
• Inspect venting and intake: Even partial blockage can cause the pressure switch to open during burner operation. Check the full length of PVC vent and intake for sags, water accumulation, or obstructions.
• Check condensate trap: On high‑efficiency Fraser‑Johnston furnaces, a partially plugged condensate trap can cause fluctuating pressure. Remove the trap, clean thoroughly, and reinstall, ensuring all hoses are tight.
• If switch tests good: The IFC board may be misreading the pressure switch signal. This requires advanced diagnosis and likely board replacement by a professional.