Normally yhis means its time to bleed. I tried to do this, actually totally removed bleed screw, but to no effect. Indeed no water came out of the bleed hole. I made sure that the pump was working (and that water was moving around the system), but what next please?
As far as I can tell. One end has thermostatic valve (showing open), other end has no valve. As far as I can remember all was well until a couple of days ago. Nothing touched!