Water heater attempts to start but shuts down with flue / exhaust error on display

Safety first: Switch off power and gas before inspecting the flue. Never operate the heater with a suspected flue blockage.

Step-by-step checks:

• Inspect outside terminal: Go outside and visually inspect the De Dietrich flue terminal. Remove any visible obstructions such as leaves, plastic bags, or snow. Ensure the terminal clearance from walls and windows meets local regulations.
• Check condensate drain: Locate the condensate trap at the base of the unit. Ensure the drain hose is not kinked or frozen. Remove the trap (if serviceable) and flush it with clean water to remove sludge.
• Verify flue connections: From inside, check that all flue joints are properly seated and locked. Look for signs of sagging or water accumulation in horizontal sections.
• Flue gas sensor check: Locate the flue gas temperature sensor on the flue outlet or heat exchanger. Ensure its connector is firmly attached and the cable is not damaged.

When to call a professional: If E03 persists after clearing obvious blockages, or if you suspect incorrect flue installation or a defective flue gas sensor, contact an authorized De Dietrich technician. Flue system modifications must comply with manufacturer and local regulations.