Heater starts then quickly shuts down with H3 error; may cycle on and off repeatedly.

Safety first: Turn off power and gas before servicing. Flame loss can cause raw gas accumulation; do not repeatedly reset the heater without inspection.

• Check for wind or ventilation issues: Strong wind or negative pressure in the equipment room can blow out the flame. Ensure the AstralPool flue terminal is correctly installed and unobstructed, and that the heater has adequate combustion air.
• Clean burners: Remove the burner tray (if accessible per manual). Use a soft brush and vacuum to remove rust, soot, and debris from burner ports. Do not enlarge the ports.
• Clean flame sensor: Gently clean the flame sensor rod with fine emery cloth to remove oxidation. Reinstall ensuring it is properly positioned in the flame.
• Inspect gas line: Check for kinks or undersized flexible connectors. Ensure all manual gas valves are fully open.

If the heater still shows H3, a professional should check gas pressure under load and test the ignition control module.