On a bosch worcester boiler, there is a water make-up tap fitted usually just below the boiler to allow the sealed radiator part of the system to be topped up or pressurised with water. However I recommend that you check your system for any leaks first. If you are sure that you dont have any leaks, then by opening the make-up valve you can top the system up until the pressure dial reads 1.5bar. At this point, close the make-up valve as too high a pressure will damage the system. You wil then need to go around all the radiators and bleed them one-by-one to expel any air. Re-check the system pressure and if necassary, open the make-up valve to restore the pressure, but do make sure that once it is at 1.5bar, you close the make-up valve. Good luck.
Chris B, July 2007
