I need urgent help. I have just cleaned my NO Nonsense filter system (similar to a magnaclean ) and I closed the valves and carefully removed the tube and washed it out. I reinserted the tube and re opened the valves etc but now my heating won't work. The flow pipe is hot but the return is cold. I opened up the filter again and removed the enner tube of the filter and the heating now works. So then once again I re inserted the inner tube and tried my heating but the flow gets hot and the return remains cold. So the filter system with the inner tube in prevents my heating working correctly but when the inner tube is taken out of the filter system, the heating works. would anyone know what on earth could be causing the problem .