Boiler displays E06, hot water temperature fluctuates or is incorrect, heating may still work

Safety first: Turn off power before accessing internal components.

• Check symptom: Run a hot tap. If the boiler attempts to fire but shuts down with E06, the DHW sensor is likely at fault.
• Inspect DHW NTC: On Sime combi boilers, the DHW NTC is usually clipped to the DHW outlet pipe or mounted on the plate heat exchanger. Check for secure mounting and intact wiring.
• Clean and reseat: If there is scale or corrosion, gently clean the contact area and reseat the sensor plug.
• Measure resistance (engineer task): Compare the NTC resistance to the manufacturer’s chart. Replace if readings are inconsistent or intermittent when the cable is flexed.
• PCB check (engineer task): If a known-good sensor still gives E06, the main PCB input may be defective and require replacement.