Display shows 'SFS' and heater will not fire; may occur on models with stack flue sensor.

Safety first: High flue temperatures can damage the heater and vent. Turn off power and gas before inspection.

Steps to address SFS error:

• Inspect venting: Check the vent pipe for obstructions, crushed sections, or improper terminations. Ensure vent size and material match Raypak specifications.
• Check for scale: Long‑term operation with hard water can scale the heat exchanger, raising flue temperatures. Look for signs of reduced water flow and overheating. Professional descaling may be required.
• Inspect stack flue sensor: Locate the sensor in the flue collector. Ensure it is firmly mounted and not hanging loose. Check wiring for heat damage or loose connections.
• Test sensor: With power OFF, disconnect the sensor and measure resistance. Compare to Raypak’s temperature/resistance chart. Replace if readings are out of range.
• Check gas input: Excessive gas input can overheat the flue. A licensed technician should verify inlet and manifold gas pressures and orifice sizing.

Warning: Do not bypass the stack flue sensor; it protects against dangerous overheating.