Boiler displays error 23, domestic hot water temperature is not regulated correctly, may be too hot or too cold.

Safety: Isolate power and water supply. Water in the DHW circuit may be hot; open taps to relieve pressure before removing sensors.

• Access DHW NTC: Locate the DHW NTC on the secondary heat exchanger or DHW outlet pipe. Ensure it is fully inserted into its pocket.
• Check wiring: Inspect the cable and connector for damage or loose fit. Reseat the connector on the PCB.
• Measure sensor resistance: Compare the NTC resistance at room temperature with Immergas specifications. Replace the sensor if readings are incorrect or intermittent.
• Descale sensor pocket: If the sensor is heavily scaled in place, carefully descale the pocket or replace the affected section to ensure good thermal contact.
• PCB check: If the sensor and wiring are good but the boiler still shows error 23 or unstable DHW temperature, the PCB may be at fault.
• Verify DHW temperature: After repair, run hot water and confirm stable outlet temperature without overshooting.