Half of our radiators are suddenly not warming up at all, although the 3 or 4 physically nearest the boiler are working fine. I’ve bled the radiators again and although they let out a small amount of air they then just stop without any water coming out. The boiler is a Vaillant gas storage (?) boiler. Any ideas as to whats wrong?? – is this something we can sort out ourselves or do we need an expert?
If no water comes out of some of the radiators, the pressure is too low in the system to push water into the radiators. There is usually a fill valve to the system. If there is one, and the valve to the system is open, the valve can be clogged, so it would need repair. If the valve is closed, open it and see if water enters the system. The pressure gauge should indicate some pressure around 12-15 psig. To go further than this requires the services of an experienced heating plumber.