F75 points to a few possible problems, hopefully for you not too serious.
There are four buttons under the display, the top left one resets the boiler, while the boiler is going through its start up check, press the bottom left ( - ) button, this will tell you on the display how much pressure is in the boiler (measured in bars), if it's below 1.0, top it up until it reaches between 1 & 1.5bar Just keep pressing the minus button to see the pressure.
If that doesn't sort it and F75 re-appears, you will need to call someone in, as either the pressure sensor or pump will be faulty.
Carefree, January 2011
