Where you pocking the flexi hose with the system full by any chance - just how wet did you get.
If you're system is that blocked and gungy, then there's a good chance that the whole system is as well, and I suspect there's cold patches at the bottom of the radiators. At some stage, you'll need to drain the whole system down, and progressively flush the system through.
You first put some system cleaner in the Central heating and run it for about a week, then you can hire power flushing machine, but if you're not a plumber, then they can be tricky to link in to the system.
As you spotted earlier, if you move the crud, you've got to get it to go somewhere, so If you do it manually then you take off the rads, carry them outside (careful to make sure no water drops on the carpets, and put a hose on one end, and run water through it - but you need to thump it, and try and turn it upside down at the same time to dislodge the crud in the bottom, and you do each one in turn before starting on the pipes. This bit gets tricky, as you have to have a hose from the mains tap on one of the rad valves, then you put a hose on another valve further down the system, and stick that in a big bucket. You shout at your assistant to tun on the water, and the crud get pushed down the pipe, and out of the hose in to the bucket you're holding. and you just keep moving round the system till you get no more crud coming out. You put the rads back on, fill the system, add the inhibitor, and you should have a much better system.