Boiler shows A6; may run at reduced output or shut down

Safety: Isolate power before working on wiring. This fault usually does not affect basic safety but can impair efficiency and comfort.

• 1. Check system configuration: Confirm that the Buderus boiler is configured to use an outdoor sensor. If no sensor is installed but the control is set for weather compensation, an A6 fault may appear.
• 2. Inspect outdoor sensor: Locate the Buderus outside temperature sensor on the north or northwest wall. Check for physical damage, water ingress, or paint covering the sensor.
• 3. Wiring check: Follow the low-voltage cable from the sensor back to the boiler or Logamatic control. Look for cuts, joints exposed to moisture, or loose terminals.
• 4. Resistance measurement: Disconnect the sensor and measure resistance. Compare to Buderus outdoor sensor chart. Replace if readings are not plausible for the current outdoor temperature.
• 5. Control setting: If no outdoor sensor is used, disable weather-compensated mode in the Buderus control menu (or fit the correct sensor).
• 6. Control board: If a known-good sensor and wiring are present but A6 persists, the control module may be defective and should be checked by a technician.