Display shows A61; unit may lock out and not respond to demand.

Safety: Turn off power and gas. Allow the heater to cool completely before touching internal components.

• Check ventilation and clearances: Ensure the heater has adequate ventilation and that louvers and air inlets are not blocked. Overheating can trigger internal safety sensors.
• Locate internal sensor: Refer to the Buderus service manual to identify the internal safety or limit sensor location on the heat exchanger or internal frame.
• Inspect mounting: Confirm the sensor is firmly attached and making good contact with the surface it monitors. Tighten mounting screws if loose.
• Test sensor: Disconnect and measure resistance. Compare with Buderus specs. Replace if readings are abnormal.
• Check for signs of overheating: Look for discoloration, melted insulation, or burnt smells around the sensor and nearby wiring. Address root causes such as blocked vents or fan failure.
• Reassemble and test: After replacing any faulty sensor, restore power and gas, clear the error, and monitor operation to ensure the A61 code does not recur.

If the sensor tests good but the error persists, the control board may be defective and should be evaluated by a professional.