I am having a problem refilling my stystem after empytying it. The water will not fill the rads from the expantion tank. The system is running off a back boiler

paul, January 2008

Sonds like an Air lock is causing the problem, either take the bleed valve out of Rad so air can move faster this might work it did for me in last house, when the air lock moves the water will shoot out so be ready, or connect mains cold water and blow water back up into the system if possible

Roger Brown, January 2008