BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to try first
Locate the filling loop, which is usually a flexible silver hose with one or two valves underneath the boiler.Gradually open the valve(s) to let mains water into the system while watching the boiler's pressure gauge.Stop filling once the needle reaches the green zone, typically between 1.0 and 1.5 bar, then tightly close the valve(s).
02
F.00 High Engineer
Your boiler has stopped working because it has lost the connection to the sensor that monitors the temperature of the water flowing through your heating system.
Full guide for F.0003
F.01 High Engineer
Your boiler has lost the signal from the sensor that monitors the temperature of the water returning to the unit, causing it to shut down for safety.
Full guide for F.0104
F.10 High Engineer
Your boiler has stopped working because a sensor that measures the water temperature is providing an incorrect electrical signal that the system cannot understand.
Full guide for F.1005
F.11 High Engineer
Your boiler has identified a faulty electrical signal from the pipe that carries water back from your radiators, preventing it from heating your home reliably.
Full guide for F.1106
F.20 High Engineer
Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage.
Full guide for F.20on the Vaillant ecoTEC Pro 30
Pressure relief valveExpansion vesselPressure sensorNTC Flow Temperature SensorWiring harnessReturn NTC thermistor
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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