Tankless water heater powers on but does not fire; display shows E0 and unit will not enter normal operation.

Safety first: Turn OFF power at the breaker and close the gas shutoff valve before removing any covers. Allow the unit to cool completely.

• Inspect wiring harness: Remove the front cover of the Richmond tankless heater. Locate the harness between the main control board and the front display/control panel. Check for loose plugs, bent pins, or corrosion. Reseat each connector firmly.
• Check for moisture or corrosion: Look for signs of water intrusion around the control board area. If you see rust or white corrosion on connectors, dry the area thoroughly and clean light corrosion with electrical contact cleaner.
• Reset the unit: Restore power, then press and hold the power button (or reset button if equipped) for 5–10 seconds. If E0 clears and the unit operates normally, monitor for recurrence.
• Board inspection: With power OFF again, visually inspect the main PCB for burnt spots, swollen capacitors, or cracked solder joints. If any damage is visible, the board should be replaced.
• When to call a pro: If E0 persists after reseating connectors and resetting, replacement of the main control board or display module is likely required and should be done by a qualified technician to ensure proper gas and ignition safety checks.