Baxi E78 Fault

Baxi E78 Fault

The Baxi E78 error code relates to a water pressure sensor fault. This code indicates that the boiler’s control system has detected an issue with the sensor responsible for monitoring the water pressure within the system. The fault may cause the boiler to misread the system’s actual water pressure, leading to operational problems or a complete shutdown to prevent damage or unsafe conditions.

Causes of the E78 Error Code

  1. Faulty Pressure Sensor: The sensor itself may be malfunctioning or damaged, leading to incorrect pressure readings.
  2. Wiring Issues: Faulty or loose wiring connections between the pressure sensor and the boiler’s control unit can disrupt the transmission of accurate pressure readings.
  3. Sludge or Debris: Accumulation of sludge or debris in the system can affect the pressure sensor’s ability to accurately detect water pressure.
  4. Airlocks: Air trapped within the heating system can influence water pressure readings, potentially leading to the E78 error.

Troubleshooting and Resolving the E78 Error Code

  1. Inspect the Pressure Sensor: Check the pressure sensor for any visible signs of damage or corrosion. If the sensor appears to be faulty, it will need to be replaced by a professional.
  2. Check Wiring Connections: Ensure that all wiring connections between the pressure sensor and the boiler’s control unit are secure and in good condition. Loose or damaged wires should be repaired or replaced.
  3. Bleed the System: Bleed radiators and the heating system to remove any trapped air, which might be affecting pressure readings.
  4. System Flush: Consider having a Gas Safe registered engineer perform a system flush to clear sludge or debris that could be impacting the sensor’s operation.
  5. Reset the Boiler: After addressing potential issues, reset the boiler to clear the error code and retest the system. A reset can sometimes resolve temporary sensor faults.
  6. Seek Professional Help: If the E78 error persists or you’re unsure how to proceed, it’s advisable to contact a Gas Safe registered engineer for a comprehensive diagnosis and repair. A professional can accurately determine whether the pressure sensor, wiring, or another component is at fault and carry out the necessary repairs safely.
  7. Regular Maintenance: To prevent future occurrences of the E78 error and other issues, ensure your boiler and heating system receive regular professional maintenance. This can help identify and resolve potential problems before they lead to fault codes or system breakdowns.


The Baxi E78 error code signifies a water pressure sensor fault that requires attention to ensure the boiler operates efficiently and safely. While some basic checks and system maintenance can be performed by the homeowner, diagnosing and repairing sensor and wiring issues typically necessitates professional intervention. Regular servicing by a qualified technician can help maintain the system’s reliability and prevent similar faults.