How to fix boiler (saunier duval) leak?

Hi there,
I've got a little problem with my boiler. What happened when the hot water suddenly disappeared (whilst being left in charge of my host family's house ). I was told to open some tap to get the pressure back up to 1.5bar. Only not knowing what I was doing, left it too long (until 2bar). I therefore opened another tap to let out the excess water coming out from a rubber pipe. I was able to get back hot water only now there is a constant dribble from the same pipe making the pressure decrease and cutting the hot water. ???? Pleaseee help me!
Thank you very much