central heating problem driving me crazy. i have wall hung system boiler with indyrect cylinder. all upstairs 4 rads get hot. there are two rads in kitchen on drops which get hot. there are 4 rad down stairs which are on a run under concrete floor. the 1st one gets hot 2nd and 3rd dont really. hot at top cool at bottom. 4th one gets hot. have had sludge remover done. no change. might b air locked in pipe wk so had auto matic air vents in cylinder cupboard and two high points for air to work its way to. still no change. finally had 2nd and 3rd rads replaced with new ones and pipe work brought down on drops to them. still no change but little better. at total loss. need help. is the pump not powerful enough? pump does work.