Bradford White electronic gas water heater shows E20; unit may not respond to thermostat changes.

Safety: Turn off power at the breaker before touching any wiring or control boards.

Steps:

• Power reset: Turn off power for at least 5 minutes, then restore. Sometimes transient faults clear with a hard reset.
• Check supply voltage: Verify the heater is receiving correct line voltage (120V or 240V depending on model). Low or fluctuating voltage can cause control errors.
• Inspect board: Remove the control cover and visually inspect the control board for burned components, bulging capacitors, or corrosion. Ensure all harnesses are fully seated.

Control board replacement is typically required for persistent E20 faults and should be performed by a qualified technician to ensure correct configuration and safe operation.