WHY IS MY BOILER LEAKING?

My boiler, (a Glow worm 45-60 B) has started to leak water from the main inside bit (where you can unscrew a little door thingy),That's the technical term!Also there is excess steam coming out of the vent when heating water.Oh ,and the heating stopped working just before xmas.I'm too scared to call anyone out unless it gets condemned as i'm financially challenged at the mo' .Can anyone give me a glimmer of hope?