Water heater locks out with E05; burner shuts down during operation, often after running for several minutes.

Safety: Turn OFF power and allow the unit to cool. Water inside may be extremely hot.

• Check water flow: Ensure all hot water fixtures have normal flow. Clean faucet aerators and showerheads. Verify the Alpha cold water inlet filter screen is not clogged.
• Inspect temperature sensors: Locate the Alpha outlet (hot) NTC thermistor on the heat exchanger outlet pipe. Check for loose connections or damaged wiring.
• Descale heat exchanger (if applicable): If the unit is a tankless Alpha model, connect a pump and hoses to the service valves and circulate a manufacturer-approved descaling solution through the heat exchanger following the Alpha service instructions.
• Reset high limit: Some Alpha storage-type heaters have a manual reset high-limit thermostat behind the access panel. Press the red reset button if tripped. If it trips repeatedly, do not continue to reset—find and correct the cause.

Persistent E05 after cleaning filters and descaling indicates a likely failed sensor or high-limit device; replacement should be done by a professional.