lennie m3bsm

Hi , i have outback 2004 3.0 with problem with the low water level in my radiator it needs to be topped up or it fills my expension bottle. i changed the thermostat as the old one was siezed. should i change the water pump and all the hoses or the pipes from the heater matrix. p[lease can you help as my subaru dealer cant help me much !!!!! thanks lennie