I bled our downstairs radiators with no problem. The upstairs radiators would not bleed. After this , the hot water failed & i noticed the combi pressure gauge read 0 bar. A sticker on the combi says that the reading should be at least 1 bar. The combi is made by "ideal", & says "isar" on the control panel. Thanks to anyone who replies.
When you bled your radiators you also released the pressure in the system, to increase the pressure you must locate the filling loop which will be located near the boiler (most of the time) use this to increase the pressure in the system. you can then bleed the rest of the rads but remember to check the pressure after the have been bled and set it correctly