This is a very strange problem that has my plumber friend very confused. When the boiler is on, the pressure holds constantly at between 1.5 and 2 bar for about 2 weeks. Without warning, the pressure will read ‘0’ and the heating goes off. When I add more water to the boiler system, to bring it back to 1 bar (so that it fires up), within 30 minutes, the boiler reads between 3 and 3.5 bar of pressure. I remove water from a radiator to bring the pressure down to 1.5 and it runs happily again for another 2 weeks. I have to run the heating on continuous to keep the pressure in the system

Andy Barrington, January 2015

Have you checked the expansion vessel pressure,this can only be done when the system pressure is 0

toptrish, January 2015