Baxi E1 Fault

Baxi E1 Fault

The Baxi E1 error code, often followed by another number (such as E1 19, E1 31, etc.), typically indicates an issue related to the boiler’s temperature sensors, known as NTC (Negative Temperature Coefficient) thermistors. These sensors monitor the water temperature within the boiler and the heating system, and discrepancies or faults in their readings can lead to various operational issues. The specific nature of the problem can often be identified by the numbers that follow the E1 code.

General Causes of E1 Error Codes

  1. Faulty Thermistor: A thermistor can fail due to age, wear, or damage, leading to incorrect temperature readings.
  2. Wiring Issues: Loose or damaged wiring connections between the thermistor and the boiler’s control board can cause erroneous signals.
  3. Sludge or Scale Build-up: Accumulation of sludge or scale in the system can affect water temperature around the thermistor, leading to inaccurate readings.
  4. Poor Circulation: Issues with system circulation can affect the temperature detected by the thermistor, potentially due to pump problems or airlocks.

Common E1 Error Code Variants and Troubleshooting

  • E1 19 (Flow NTC Fault): Indicates a problem with the sensor that measures the temperature of the water leaving the boiler. Check the sensor and wiring for damage, and ensure there’s no sludge affecting its readings.
  • E1 20 (Return NTC Fault): Points to an issue with the sensor measuring the temperature of water returning to the boiler. Similar checks as for the flow NTC fault apply.
  • E1 31 (Supply Voltage Too Low): While not directly a thermistor issue, this code indicates that the boiler is experiencing low electrical supply voltage, which could affect sensor operation.

Resolving E1 Error Codes

  1. Inspect and Clean Thermistors: If accessible, inspect the thermistors for any signs of damage or build-up. Cleaning the sensor can sometimes resolve the issue.
  2. Check Wiring Connections: Ensure all connections between the thermistors and the control board are secure and free from damage.
  3. Bleed the System and Check Circulation: Address any circulation issues by bleeding radiators to remove airlocks and checking the pump’s operation.
  4. Reset the Boiler: After addressing potential issues, reset the boiler to clear the error code and retest the system.
  5. Professional Assistance: Due to the technical nature of diagnosing and repairing issues related to NTC thermistors and electrical components, it’s advisable to consult a Gas Safe registered engineer for accurate diagnosis and safe repairs.
  6. Regular Maintenance: Prevent future occurrences of E1 error codes through regular professional maintenance. This ensures that thermistors, circulation pumps, and other critical components are in good working order.


The Baxi E1 error code highlights issues related to temperature sensing within the boiler system. While homeowners can perform basic checks, resolving the underlying cause often requires professional intervention. Regular maintenance can help prevent such issues, ensuring efficient and reliable boiler operation.