Unit displays E03 and shuts down; burner stops shortly after ignition attempt or will not light at all.

Safety warning: Turn off electrical power and close the gas shutoff valve before servicing. Combustion components can be hot.

• 1. Confirm gas supply stability: Check that other gas appliances are not causing pressure drops (e.g., multiple large appliances starting at once). If you suspect gas supply issues, contact your gas utility.
• 2. Inspect and clean burner: Remove the burner access panel. Carefully remove the burner assembly following the Triangle Tube service instructions. Use a soft brush and vacuum to remove dust, lint, and debris from the burner head and mixing area. Do not damage burner ports.
• 3. Clean flame sensor: Remove the flame sensor rod. Clean it with fine abrasive pad until bright metal is visible. Reinstall and ensure the sensor is properly positioned in the flame path.
• 4. Check grounding and wiring: Verify the appliance ground connection is tight and corrosion-free. Inspect the flame sensor wire and connector back to the control board for damage or loose fit. Reseat connectors.
• 5. Observe flame: With panels reinstalled and gas/power restored, run the heater and observe flame through the sight glass. The flame should be stable and blue. If it lifts off the burner or goes out when the circulator changes speed, there may be a gas valve or combustion air issue.
• 6. Gas valve and control: If E03 recurs after cleaning and wiring checks, the gas valve or main control board may not be maintaining stable flame current. These components should be tested and replaced only by a qualified technician.