Heater ignites but produces excessive soot on the flue terminal or heater casing.

Safety first: Turn off gas and power. Sooting indicates unsafe combustion and can lead to carbon monoxide production.

Step-by-step checks:

• Check combustion air openings: Ensure that louvers, grilles, and vents supplying air to the heater are not blocked by debris or stored items.
• Inspect burner: Remove the burner tray and clean all ports with a soft brush and compressed air. Do not enlarge the ports.
• Verify flue is clear: A partially blocked flue can cause poor draft and sooting. Inspect and clear as needed.
• Gas pressure and orifices: A gas technician should measure manifold pressure and verify that the correct orifices are installed for the gas type (natural or LPG) and altitude.

When to stop: Do not operate a sooting heater. Have a qualified technician perform a full combustion analysis and adjustment.