Hi the problem with your heater is prob down to the lack of coolant in the system caused by the leaking water pump. add the rad weld, top up the coolant, turn the heater temp switch to full (hot) run the engine with the pressure filler cap off, keep the coolant topped up whist running the engine untill the cooling fan cuts in and out again. switch off engine, top up coolant refit the pressure cap. (Radweld will only stop the leak for a short period of time) Hope this helps. Dean (www.Larkins-AutoServices.co.uk)