still got cold radiators

[woodchip40]

i'm new here and i'm at my wit's end. allow me to tell the history to date. gravity fed central heating with expansion tank in loft of bungalow. last month when i fired up the syatem we only got a few rads warm nearest the boiler.i added 'x400' for a week, i drained the system at every low point, refilled and added inhibitor. no chnage !
i then bought a new grundfos 15-60 circulation pump. no change !
i then drained system , added 'x400' again for a week, drained system and refilled , this time - worse- the rads that were heating up were no longer getting hot !
i hired a power flush machine, followed all instructions and spent the whole weekend flushing - it was amazing how much thick brown liquid came out. i finally got the rads hot all round the house with thi power flush connected. 'great' i thought, so i refitted my new grundfos pump back into the system. all things put back to original settings and fired up the boiler.- i am so disappointed that the radiators are not getting hot. it ias as if i had not done anywork at all. only the first 2 rads nearest the boiler are getting hot.
i can only assume the grundfos pump ( which is brand new) is not powerful enough to pump the water round. i haven't got much money left so i cannot afford to get the system replaced.
i am asking on here for any advice that may help me. i would like to know if i can fit another pump( same as my new one) further round the system and wire it up in parallel with the original one. in so doing would this double the 'push' of water around the system ?
regards and hoping i can get it sorted before the inlaws come for christmas.

 

[xr4x4]

anyone been messing around with the lock shield valves on the rads?

if you turn off all the rads but one, does that one get hot all over? try this with all of them.

what speed is the pump on?