How to Fix / Troubleshooting

Scalding risk: Allow system to cool before topping up water. Monitor 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 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.

E09 error; controller indicates low water pressure or lack of water in system

Possible Causes