Display shows E03 and the water heater shuts down shortly after start, 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 cause is identified.

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

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