The in car heater has stopped working. The pipes in the engine bay that feed the heater remain cold as does the bottom hose from the radiator. The top hose to the radiator is really hot. The radiator is not blocked. Is this due to the thermostat not working, or could it mean that the water pump is faulty.
The coolant needs topping up after about 400 miles.

Steambuff, January 2011

Thanks John I'll try bleeding the system before tackling the thermostat option.

Steambuff, January 2011

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