While you wait for answers, we may have found some information which could help you.
Click here for Vaillant Water Heating Working
Problem with the pressure in combi boiler?
Vaillant VCW-Sine18 T3WFH Lights but then goes off after 5 Min?
Vaillant F22 fault?
Vaillant 828E - no hot water?
Vaillant vcw gb242 eh central heating problem?
Vaillant ecotec 831 plus?