A8
Buderus
Return Temperature Sensor Fault
Display shows A8, furnace may run at reduced output or shut down intermittently
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Defective Buderus return temperature sensor, Loose or corroded sensor connector, Damaged sensor cable, Sensor not properly seated in return pipe
How to Fix / Troubleshooting
Safety: Disconnect power before opening the control or piping access panels.
Steps:
- Locate return sensor: The return NTC sensor is usually installed on the return water pipe entering the Buderus heat exchanger or hydraulic block.
- Inspect wiring and connector: Check for loose plugs, corrosion, or damaged insulation. Reseat the connector on the control board.
- Check sensor mounting: Ensure the sensor is fully inserted into its well or firmly clamped to the pipe with thermal paste if required.
- Resistance test: With power off, disconnect the sensor and measure resistance. Compare to Buderus specifications for the approximate water temperature. Replace if readings are far off or open/shorted.
After correcting wiring or replacing the sensor, restore power and verify that the A8 code clears and the furnace operates normally.
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Repair Difficulty
Medium
3/5
Required Part
Buderus Return Temperature Sensor (NTC)
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