Boiler displays E19, burner stops, error may appear intermittently.

Safety: Isolate power before accessing sensors and wiring.

• Locate return sensor: Find the NTC sensor on the return pipe entering the boiler heat exchanger.
• Check mounting: Ensure the sensor is firmly clamped to the pipe with good thermal contact and insulated from ambient air.
• Inspect wiring: Look for damaged insulation or loose plugs at both the sensor and control board.
• Measure resistance: Compare the NTC resistance with the Klimosz chart. Replace if readings are incorrect.
• Test operation: After replacement, reset the boiler and monitor return temperature readings if available.