Ariston 304 Fault

Ariston 304 Fault

The Ariston error code 304 indicates a fault with the Domestic Hot Water (DHW) temperature sensor. This sensor monitors the temperature of the hot water supplied to taps and showers. A malfunction or discrepancy in the readings from this sensor can affect the boiler’s ability to correctly regulate the temperature of the hot water, potentially leading to water that is too hot or too cold.

Causes of Error Code 304

  1. Faulty DHW Temperature Sensor: The sensor itself may be malfunctioning, damaged, or incorrectly calibrated, leading to inaccurate temperature readings.
  2. Wiring Issues: Problems with the electrical connections between the DHW temperature sensor and the boiler’s control unit can cause faulty readings.
  3. Sludge or Scale Build-up: Accumulation in the hot water system, particularly around the sensor, can impact its ability to accurately measure water temperature.
  4. Improper Sensor Placement: If the sensor is not correctly positioned within the hot water system, it may not accurately detect water temperature.

Troubleshooting and Resolving Error Code 304

  1. Inspect and Clean the Sensor: Check the DHW temperature sensor for any signs of damage or buildup. Carefully clean the sensor to ensure it can accurately measure water temperature.
  2. Check Wiring Connections: Ensure all connections between the sensor and the boiler’s control unit are secure and in good condition. Repair or replace any damaged wiring.
  3. Adjust Sensor Placement: Verify that the DHW temperature sensor is correctly positioned as per the manufacturer’s instructions. Adjustments may require professional assistance.
  4. Flush the Hot Water System: Consider having a professional flush the hot water system to remove any sludge or scale that could be affecting the sensor’s performance.
  5. Reset the Boiler: After addressing potential issues, reset the boiler to see if the error clears and normal operation resumes.
  6. Professional Diagnosis and Replacement: If the problem persists or you’re unsure how to proceed, consult a Gas Safe registered engineer. A professional can accurately diagnose the issue and replace the DHW temperature sensor if necessary.
  7. Regular Maintenance: To prevent future occurrences of error code 304 and ensure the efficient operation of your hot water system, schedule regular maintenance checks with a qualified technician. This can help identify and resolve potential issues early.


The Ariston error code 304 is a clear indicator of a problem with the Domestic Hot Water temperature sensor, requiring prompt attention to maintain the proper functioning of your hot water supply. While homeowners can perform basic checks and cleaning, more complex issues related to sensor functionality or system buildup typically necessitate professional intervention. Regular maintenance is essential for preventing such faults and ensuring the longevity and reliability of your heating and hot water system.