Well if the TRVs are good and the lockshields are wide open, try turning off all the other radiators (The ones that are working) to see if you can force the water into the two that are not working, this will also help to clear any air-locks that may have formed...
If the rads still don't get hot, then you'll be looking into checking for a blockage somewhere, if they then get nice and hot, try turning the others back on again, if all is well, it was an air-lock... If they die off again, you need to get your system re-balanced.
GasAid.co.uk, December 2006
