BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has automatically shut down because the internal water pressure has dropped too low to run safely.
What to try first
Locate the filling loop (two valves connected by a flexible silver hose under the boiler).Open both valves slowly to let mains water into the system.Watch the pressure gauge on the front of the boiler until the needle rises into the green zone (between 1.0 and 1.5 bar), then firmly close both valves.
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.12 High Engineer
Your boiler is struggling to detect the temperature of your hot water due to a wiring issue or a faulty sensor, so it has stopped heating to prevent potential damage.
Full guide for F.1206
F.20 High Engineer
Your boiler has temporarily shut down because the internal water temperature got too high.
Full guide for F.20on the Vaillant ecoFIT sustain 615
Pressure sensorExpansion vesselManual filling loopFlow 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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