Put the thermostat in a saucepan of water and bring towards the boil. You should see the thermostat open if it is working. You could try running the car without the thermostat in for a few days, to confirm that the engine does not overheat, before looking to replace the water pump. Your question says that the top radiator hose gets hot. What about the bottom one? Is there a bleeding point in the system for releasing trapped air?
Poacher John.
January 2011