RAadiators getting hot with heating controls turned off?

Just moved in to new home and noticed when Heating/water pump kicks in all the radiators in the house are getting hot even when the heating thermostat is turned right down and also when the water and heating honeywell controls are turned to the off position. The problem is really noticable at night when the heating is not required but as soon as I hear the water pump start to circulate then the radiators are getting hot. Could it be the three way valve passing?

Allan
December 2010