What does the Baxi 600 Series E840 fault code mean?
The E840 fault code on the Baxi 600 Series indicates a lockout condition in the domestic hot water (DHW) system. This typically means that the boiler has detected a fault that prevents it from heating water effectively.
Common Causes
- Blocked DHW Heat Exchanger: A blockage can prevent hot water from circulating, leading to a lockout.
- Faulty DHW Sensor: If the sensor that monitors water temperature fails, it can trigger a lockout to protect the system.
Can I fix it myself? (DIY)
It is recommended to call a Gas Safe Engineer for any issues related to gas or electrical components. However, if you suspect a blockage, you may check the filters and ensure the system is free from debris.
Estimated Repair Cost (2026 UK Prices)
The estimated repair cost for resolving the E840 fault could range from £150 to £300, depending on whether a sensor replacement or heat exchanger cleaning is required. This estimate includes parts and labour for a qualified engineer.