Boiler shows E06; may continue to run at reduced performance or shut down depending on model.

Safety: Disconnect power before removing panels.

• Find the return sensor: The return temperature sensor is usually mounted on the return pipe or lower manifold of the IBC boiler.
• Inspect connection: Verify the sensor plug is fully seated on the sensor and at the control board. Look for corrosion or moisture at the connector.
• Check cable routing: Ensure the cable is not rubbing against hot surfaces or sharp edges that could cause intermittent shorts.
• Reset: After reseating connections, power the boiler and clear the error. Monitor if E06 reappears.

If the error persists, the return sensor should be replaced with the correct IBC part. If that fails to resolve the issue, the main control board may be defective and should be evaluated by a technician.