Control shows A7, burner shuts down or will not start, temperature readings seem incorrect

Safety: Turn off power to the furnace before accessing the control compartment.

Steps:

• Locate the flow sensor: On Buderus furnaces, the flow temperature sensor (NTC) is typically mounted in a well on the supply (flow) pipe near the heat exchanger.
• Check wiring: Inspect the sensor harness from the NTC to the Buderus control board. Ensure the plug is fully seated and wires are not pinched or damaged.
• Inspect sensor placement: Confirm the sensor is fully inserted into the sensor well and secured with its clip or retaining screw.
• Basic resistance check (if you have a multimeter): With power off and sensor disconnected, measure resistance across the sensor terminals. Compare to Buderus temperature/resistance chart. An open (infinite) or shorted (near 0 Ω) reading indicates a bad sensor.
• Reset control: After reseating connections, restore power and clear the error by cycling power or using the reset function if available.

If A7 returns, the flow temperature sensor should be replaced with an OEM Buderus NTC sensor.