how can i fix my f75 fault on vaillant ecotec plus ?

F.75 indicates one of two possible faults.
Either the pump has failed (used to be a problem with earlier models), or more likely the pressure sensor has acted.

It could be down to C/H pressure.

Press the minus button (bottom left of the 4 buttons below the display where f.75 is showing), a value in digits will appear, if the reading (in bar) is less than 1.0 then the system needs re-pressurising.
If the reading is 1.0-1.5 more likely the pressure switch has a blockage and could need cleaning/replacing.

Carefree
July 2010