2 rads wont heat, i have diagnosed everything i can think of?

i have 2 radiators that wont heat at all, they are the 2 furthest from the boiler, both with relatively new trv's which arent sticking, i bled each rad with both valves closed, then opened each individually and pressure came back, so all 4 valves connect the system pressure in the pipework into the radiator, i have tried closing every other rad valve as well as putting the system pressure up to 2 but the flow pipe to these last 2 never warms up more than a few inches beyond its join with the previous radiator, which suggests there is some kind of blockage, but my test of each valve suggests not..
this is really doing my head in, am i missing something simple????
thanks