BoilerFaultCodesVaillant F18 Fault Code
The Vaillant F18 fault code means: your boiler's control panel has lost communication with the internal system, preventing you from adjusting settings or seeing the boiler's status.. It appears on 2 Vaillant models in our database.
Technical description: Local user interface fault
What causes the Vaillant F18 fault?
This fault occurs when the communication link between the display panel you interact with and the boiler's main internal brain is broken. The most common reason is a loose or damaged connection on the internal wiring, though it can also be caused by an electronic component on one of the control boards failing due to age.
DIY fix possible
Locate the main power switch for the boiler (fused spur).Turn the power off for 60 seconds.Turn the power back on to see if the control panel restarts and clears the error.
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Gas Safe Register →Vaillant models that show the F18 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F18 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026