We may have found other answers which could help you.
Click here for Vaillant Hello 18how do I rectify the fault as detailed below?
Vaillant condensing boiler ecoTEC plus?
What does f.25 mean?
how to fix water pressure its down at bottom of grey part?
Vaillant F22 fault?
vaillant ecoTEC plus boiler fault code - how to fix?