HI I HOPE SOMEONE CAN HELP,I AM TRYING TO BLEED MY HEATING SYSTEM AFTER CLEANING OUT THE D/ STAIRS RADIATORS BUT IM HAVING NO LUCK , THE SMALL WATER TANK IN THE LOFT DID NOT EMPTY AFTER DRAINING THE SYSTEM I PRESSUME IT IS AN AIRLOCK OR A BLOCKAGE BETWEEN THE TANK IN THE LOFT AND THE BOILER ITSELF,WHAT IS THE BEST WAY TO CLEAR THIS? MY SYSTEM HAS NOT GOT THE LOOP BLEEDING FUNCTION