BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has stopped working because the amount of water circulating inside the heating system has dropped too low.
What to try first
Locate the filling loop (a flexible metal hose) underneath your boiler.Open the valves on the filling loop to allow cold mains water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches between 1.0 and 1.5 bar.Close both valves tightly and remove the filling loop if required by your specific model.
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 detected that it is running much hotter than it should be and has automatically switched itself off to prevent permanent damage.
Full guide for F.20on the Vaillant ecoFIT pure 612
Pressure relief valveExpansion vesselPressure sensorFlow 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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