Unit displays E13 and shuts down; may be associated with very high exhaust temperatures.

Safety: Turn OFF power and gas. Do not operate the heater until the cause is identified.

• Check venting: Inspect the Alpha exhaust vent for blockages, sagging sections, or improper materials. Correct any visible issues.
• Descale heat exchanger: If the unit is tankless, perform a full descaling procedure using service valves and a pump, following Alpha guidelines.
• Inspect flue sensor: Locate the flue gas temperature sensor on the exhaust collector. Ensure it is firmly mounted and wiring is intact.
• Professional combustion check: A technician should verify combustion with an analyzer and confirm gas input and air settings are within Alpha specifications.

Because flue overtemperature can damage the unit and venting, have an Alpha-certified technician verify safe operation before returning the unit to service.