How can I fix my boiler; its a BIASI M9624SM/C?

After my boiler was on for 5 hours my radiators and hot water have gone cold whilst the Combi is still running in the background. I have not had this problem before. The pressure is ok as it goes between 1 and a few notches above the 1 but I noticed that the temperature went from 60' down to 30'. I had a safety check done on friday and it stated the pressure and heat input was fine yet this happened a day later?!