Furnace shuts down; display shows A7 temperature sensor fault

Safety: Turn off power to the furnace. Allow the unit to cool; water in hydronic systems can be very hot.

• Locate the sensor: On Bosch hydronic furnaces/boilers, the flow temperature sensor is usually clipped or inserted into a sensor well on the flow pipe leaving the heat exchanger.
• Check connection: Inspect the sensor plug at the control board and at the sensor. Reseat the connector and look for damaged or pinched wires.
• Test the sensor: Disconnect the sensor and measure its resistance with a multimeter. Compare to the Bosch NTC resistance chart (e.g., around 10 kΩ at 25°C, depending on model). If reading is open, shorted, or far off spec, replace the sensor.
• Reinstall properly: Ensure the sensor is fully inserted into the pocket or firmly clipped to the pipe with good thermal contact.

If a known-good sensor still triggers A7, the control board may be faulty and should be diagnosed by a professional.