We have a 'piggy backed' radiator which is cool at the bottom & warm at the top. Have tried bleeding probably a couple of pints of water with no sign of 'air' coming out -yet still feels the same.....Any help would be appreciated....
Ok. Quite possibly it's not getting its fair share of the hot water. You may need to balance the rads, or at the very least, turn down the lockshield valve (opposite end to the TRV with the numbers on it) on the nearest rad(s) to the affected one.
Try turning off a couple of the nearest rads to see if this one gets a good supply all of its own.