Ferroli Modena 80 E?

My boiler has not been giving hot water for 3 months. It just alternates between luke warm and freezing with a very occasional highlight of hot for a few seconds when it is in the mood. I adjusted the pressure to 2 and then to 2 and a half but that did not work. This morning I thought I would put it up to 3 and see if that worked but the pointer zoomed up to 4 (the maximum) all by itself it seemed and now I have luke warm central heating as well as luke warm water. Can anyone tell me how to get the pressure down again?