BoilerFaultCodesThe 6 most common faults
01
F.00 High Engineer
Your boiler has lost the signal from one of its internal temperature sensors, so it has shut down to prevent overheating.
Full guide for F.0002
F.01 High Engineer
Your boiler has lost the signal from a temperature sensor that monitors the water returning to the system, causing it to stop heating as a safety precaution.
Full guide for F.0103
F.10 High Engineer
Your boiler has detected an electrical fault in a temperature sensor, which is preventing it from safely monitoring the water heat levels and stopping it from operating.
Full guide for F.1004
F.11 High Engineer
Your boiler's temperature-monitoring system has detected a faulty signal, likely due to a loose wire or a broken sensor, preventing it from heating your home safely.
Full guide for F.1105
F.13 High Engineer
Your boiler is struggling to read the water temperature in your hot water tank due to a loose wire or a faulty sensor, so it has shut down the heating to prevent issues.
Full guide for F.1306
F.20 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for F.20on the Vaillant ecoTEC Plus 610
NTC temperature sensorWiring harnessReturn NTC sensorFlow temperature sensor (NTC)NTC Temperature SensorWiring Harness
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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