The display shows E03, and the water heater shuts down shortly after startup; the fan may run briefly.

Safety: A flue fault can lead to dangerous exhaust gas spillage. Do not operate the heater with an E03 fault until the underlying cause is identified and corrected.

• 1. Inspect flue terminal: From outside, visually check the ACV flue terminal for any obstructions such as leaves, bird nests, snow, or plastic bags. Clear any detected blockage.
• 2. Check air intake: On concentric flue systems, ensure the air intake annulus is not blocked. On twin-pipe systems, inspect the dedicated air intake pipe for any obstructions or crushed sections.
• 3. Examine condensate trap: A flooded condensate trap can restrict flue gas flow. Remove and thoroughly clean the ACV condensate trap, flush it with water, and ensure the drain hose is free-flowing.
• 4. Test air pressure switch tubing: Inspect the silicone tubes connecting the fan and the air pressure switch for any splits, kinks, or water accumulation. Drain any condensate and reseat the tubes securely.
• 5. Listen to fan operation: When the unit is starting, confirm that the ACV combustion fan runs smoothly without any grinding or squealing noises. If the fan does not start or is excessively noisy, it may need replacement.

If the E03 error persists after clearing flue/air paths and checking the tubing, the air pressure switch or fan assembly should be tested and replaced by a qualified technician.