I have exactly the same boiler and have had the same problem for months now. (Although no sticky pressure guage) Could not find any leaks anywhere and the plumber was baffled as to what the cause was. Finally last tuesday the expansion vessel blew - obviously where there water was leaking from - in spectacular fashion. Apparently Ferrolli are waiting for a shipment and dont know when they are going to be in so i still have no heating/hot water still so id order a new one now if i were you! Check to see if any water is leaking from the bottom right hand side of the boiler.
Think this is a cheap nasty boiler. Out of interest the dials that control hot water and heating temp....mine just turn without any end stop and just produce random wildly fluctuating numbers in the display window. Do you also have this problem? Seems impossible to set a temperature for either water or heating!!
Sorry to be the bringer of doom and gloom, hope it was of some help though!
Darren B
February 2010