Boiler shows E06 and shuts down shortly after starting

Safety: Turn off power before accessing internal wiring or sensors.

• Locate return sensor: On Dettson boilers, the return temperature sensor (NTC) is typically clipped or strapped to the return water pipe or inserted into a well.
• Inspect wiring: Check the sensor cable for cuts, abrasions, or pulled connectors. Reseat the plug at the control board and at the sensor if applicable.
• Check sensor mounting: Ensure the sensor is firmly attached to the pipe with good thermal contact and insulated if required by the manual. A loose sensor can give erratic readings.
• Resistance test (for technicians): A professional can measure sensor resistance at room temperature and compare it to Dettson specifications. If out of range, replace the sensor.
• Control board: If a known-good sensor still triggers E06, the boiler control board may have a defective sensor input and will need replacement by a qualified technician.