There should be a difference in temperature between the water going in and the water going out - the heat loss is going into the room! Radiators should ideally be "balanced" so that each has a temperature fall of about 10 deg C. and each radiator in the chain gets a share of the available heat. See...
http://www.miketheboilerman.com/balancing.htm
To get more heat out you might increase the temperature control on your boiler to make the water slightly hotter and adjust the speed of the circulating pump to get it round the system a little quicker.
If radiators are hot at the bottom but colder at the top they need bleeding to let any trapped air out.
Peccavi
December 2008