You say the rads are getting hot to the touch, but is that all over? i.e. the full height of the rad. If a rad does not reach an even temperature over its entire working area, this can be due to poor balancing, faulty radiator thermostats (TRVs) if fitted to your rads, worn out pump, or possibly a build up of sludge in the entire system. If that were the problem you would need to drain the entire system, possibly consider power flushing, the re-fill and check the balancing.