Error F 22 on Vaillant Boilers The F22 fault code on a Vaillant boiler indicates a low-water-pressure lockout, triggered when system water drops below the safety threshold needed to prevent a dry fire. This lockout activates as soon as water pressure falls to ≤0.6 bar on ecoTEC Plus and Pro models, or ≤0.5 bar on … Continue reading What Does the F22 Fault Code Mean on a Vaillant Boiler?