I have a primatic cylinder upstairs and a glow worm boiler downstairs and one water tank in the loft. As far as i am aware it is a single pipe system with the pump on the return. I have drained the system twice but just can't get the upstairs radiators to come on even though the downstairs ones are lovely at hot. As far as i am aware there are no balance valves on the downstairs radiators. I moved into the house last year and 2 radiators did get hot but now none of them do, Help!!