BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has temporarily stopped working because it has detected a dangerously low level of water pressure inside the system.
What to try first
Locate the filling loop underneath your boiler or check the integrated filling key.Open the valves slowly to let water into the system until the pressure gauge on the front reaches between 1.0 and 1.5 bar.Close both valves tightly and reset the boiler.
02
F.00 High Engineer
Your boiler has temporarily stopped working because it cannot accurately measure the temperature of the water leaving the system.
Full guide for F.0003
F.10 High Engineer
Your boiler has temporarily stopped working because it has detected an electrical fault with one of its internal temperature sensors.
Full guide for F.1004
F.11 High Engineer
Your boiler has temporarily stopped working because it has detected an electrical fault with one of its internal temperature sensors.
Full guide for F.1105
F.20 High Engineer
Your boiler has temporarily shut down because the internal water temperature got too high.
Full guide for F.2006
F.23 High Engineer
Your boiler has shut down because there is a dangerous difference in temperature between its internal sensors, usually caused by a restriction in water flow.
Full guide for F.23on the Vaillant ecoFIT sustain 825
Pressure sensorFilling loop valveExpansion vesselFlow temperature sensorWiring harnessReturn temperature sensor
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Vaillant shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue
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