E09 error; the controller indicates low water pressure or a lack of water in the system.
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Scalding risk: Allow the system to cool before topping up water. Monitor the pressure gauge while filling.
- Check the system pressure gauge on the boiler or nearby piping. Typical cold pressure is around 1.0–1.5 bar (follow the Defro manual).
- If low, open the filling loop valve and slowly add water until the correct pressure is reached. Close the valve securely.
- Inspect visible pipework, radiators, and valves for leaks or drips.
- Bleed air from radiators and automatic air vents, then recheck pressure and top up if needed.
- Locate the pressure sensor/switch on the boiler and check its electrical connection.
If pressure drops repeatedly after topping up, there is likely a leak or expansion vessel issue that requires a heating professional.
Repair Difficulty
Required Part
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