LED flashes four short and four long blinks; furnace shuts down unexpectedly during operation.

Safety first: Turn off power before working on condensate components.

• Clean condensate trap: Remove the plastic condensate trap assembly. Flush thoroughly with warm water to remove slime and debris. Reinstall with all hoses connected firmly.
• Clear drain line: Use a wet/dry vacuum at the drain termination to pull out clogs. Ensure the line slopes continuously downward.
• Check condensate safety switch: Some Fraser‑Johnston furnaces include a float or pressure‑type condensate switch. Verify it is not stuck in the open position.
• Inspect for leaks: Look for water inside the furnace cabinet. Persistent water issues require professional evaluation.