A Prima F boiler (generally speaking), will be fitted to an open vented system so doesn't have a filling point, it fills via the F&E cistern (probably in the loft).
It's possible that the ball valve on the system is stuck closed or the cold feed that fills the system is blocked.
However, if the system has been modified and fitted to a pressurised set up and you have a guage reading 0, the filling point should be located close to the guage, there would also be an expansion vessel nearby too.
Carefree
April 2011
howtomendit.com for free repair help, information and advice.
