problem filling bosch greenstar 28i junior?

my boiler recently lost all pressure and the hot water has stopped working properly, it comes on for about a minute then goes of for a while then back on again for about a minute. ive read many suggestions online about what could be the problem but still cannot figure it out. i tried filling the boiler with the plastic key under neath but when i twist the little tap to let the water flow, water pours everywhere. not just a little bit A LOT.

can any one help PLEASE.