Furnace displays F9, runs briefly then shuts down, may be accompanied by unusual flame behavior

Safety: Gas components must be handled only by qualified gas engineers. If you smell gas, shut off the gas supply, ventilate the area, and do not operate electrical switches.

Steps (user-level):

• Verify gas supply: Ensure the manual gas cock to the furnace is fully open and that other gas appliances in the property are working normally.
• Observe ignition: Through the sight glass, check whether the igniter glows and if the burner lights at all. If there is no flame despite ignition attempts, the gas valve may not be opening.
• Do not attempt adjustments: Do not try to adjust gas pressure or open the gas valve body. These tasks require calibrated instruments and certification.
• Call a professional: A qualified technician must test inlet and manifold pressures, verify valve operation, and replace the Ideal gas valve if necessary.