Water heater does not ignite, the burner does not start, and the display shows E01.

Safety first: If you smell gas, do not attempt any repair. Immediately shut off the gas supply, switch off electrical power to the heater, ventilate the area, and contact a qualified gas technician.

Step-by-step checks:

• 1. Reset the unit: Turn off the main electrical power switch to the ACV water heater for at least 30 seconds, then turn it back on and attempt to restart the unit. Observe if the E01 error reappears.
• 2. Check gas isolation valves: Verify that the gas cock on the ACV gas train is fully open and that any upstream building gas isolation valves are also open.
• 3. Inspect ignition electrode: Remove the burner access panel. Locate the ACV ignition electrode near the burner. Check for cracked porcelain, loose wiring, or heavy soot buildup. Clean the tip gently with fine emery cloth and ensure the electrode cable is firmly connected to the ignition transformer/control board.
• 4. Inspect flame ionization electrode: On many ACV models, the ignition and ionization functions are combined; on some, they are separate. Clean the ionization rod, ensure it is correctly positioned in the flame path, and check the cable connection to the control board.
• 5. Check gas pressure (qualified personnel only): Using a manometer on the test point of the ACV gas valve, verify that both the inlet and burner pressure match the specifications on the rating plate. If pressure is low or unstable, contact the gas supplier or a licensed gas technician.
• 6. Examine burner: Remove and visually inspect the ACV premix burner for any signs of blockage, rust flakes, or debris. Clean with a soft brush and vacuum; do not use sharp tools that could damage the burner surface.

If the E01 error persists after cleaning the electrodes and confirming the gas supply, the ignition control module or gas valve may require replacement by a certified ACV service technician.