my hot water/heatinh not working properly?

hello my heating was working but my hot water wasn't. i changed the element in the emersion heater. now neather work . the piolet light comes on. the small pump leading into the emersion heater is working all the electrics are fine. the pipes surrounding the radiators and the tank are hot. all i get is vey luke warm water. i leave the hotwater and heating switch on all day. help most appreciated, regards.