This was a repair I did on a Vaillant ecotec pro which had stopped working altogether. The display was showing the dreaded, yet extremely common F.75 fault code. The early versions of the ecotec boilers were fitted with problematic pumps and early versions of the pressure sensors also suffered from issues.
Vaillant Boiler Repair Service
Expert Gas Safe Registered Vaillant Boiler Service and Repair Specialist