Ferroli combi on the blink!

[Gambadella]

Tonight the pressure went down on my boiler. I undid the necessary valves and pushed it back up to 1.5. After a while I noticed the radiators were still cold so I went to the boiler to find warm water gushing out of the overflow and the pressure right up to 3. This carried on for while so I turned the boiler off but the water continued coming through so I've now turned the water off.
Any advice and ideas welcome...