Had a small leak on live side of valve on a towel rad. Drained system taped up not put towel rad back up. Turned off valves on towel rad. Filled system. All good. Put leak sealer in to towel rad because i lose pressure very slowly so i assume ive s miniscule leak somewhere hidden. However when i turned valves on to towel rad and turned on heating the towel rad along with one other rad didnt heat. Its not the pressure in the system that's the problem. If i bleed it for long enuff hot water cones thru. But still only luke warm. Is it possible the sealer(tec7 plumb) has blocked or partially blocked pipework?