first check there are no leaks on your system. do this by shutting off the isolation valves on your flow and return under the boiler. note the pressure and leave for an hour. if the pressure drops during this time you have a leak at your boiler. if there's no drop open the isolation valves and if it drops then you know the leak is on your system. if you had to top up your old boiler once a month I THINK THE LEAK IS ON YOUR SYSTEM.
PAULGASMAN
November 2009