Boiler displays error 79; may be associated with abnormal temperature readings or erratic operation.

Safety first: Isolate power and allow the system to cool before touching any sensors or pipework.

• Locate system sensor: This thermistor is often mounted on the heating flow or return line inside the boiler.
• Check attachment: Ensure the sensor is firmly clipped to the pipe or inserted into its pocket with good thermal contact.
• Inspect wiring: Look for cuts, abrasions, or signs of overheating along the sensor cable.
• Reset and test: After reseating connectors, restore power and reset the boiler. If error 79 persists, replace the sensor.
• Further checks: If a new sensor does not resolve the issue, the control PCB may be defective and require replacement.