Vaillant F.42 Fault Code

What causes the Vaillant F.42 fault?

This fault occurs when the boiler's internal computer stops receiving the correct electrical signals from the main wiring system. The most common reason is that the plastic connectors have vibrated loose over time or the wires themselves have developed a break or short circuit. Because the control board cannot safely communicate with the various parts of the boiler, it shuts down as a safety precaution.