Water heater does not heat properly; display shows A7 and burner does not ignite or shuts down shortly after ignition attempt.

Safety first: Turn off power to the Buderus water heater at the breaker and close the gas shutoff valve before opening the unit. Allow the unit to cool completely.

• Access the sensor: Remove the front cover of the heater. Locate the flow temperature sensor (NTC) on the outlet water pipe or heat exchanger flow line, typically clipped or threaded into a sensor well.
• Check wiring and connector: Inspect the sensor plug and wiring harness for corrosion, discoloration, or loose fit. Reseat the connector firmly. Look for damaged insulation or broken wires.
• Measure sensor resistance: With power still off, disconnect the sensor and measure resistance with a multimeter. Compare the reading to the Buderus service manual NTC resistance chart at the current water temperature. If the value is far out of range (open circuit or short), the sensor is faulty.
• Clean or replace: If the sensor is scaled or corroded, gently clean the probe with a soft cloth. If resistance is incorrect, replace the flow temperature sensor with a Buderus-approved part.
• Inspect control board connection: Trace the harness back to the main control board. Ensure the plug is fully seated and pins are not bent or burnt.
• Restore service: Reassemble the cover, open the gas valve, restore power, and clear the error by cycling power. Run hot water and verify stable operation and that the A7 code does not reappear.

If the sensor tests good but the code persists, the control board may be defective and should be diagnosed by a qualified technician.