Thought I'd add to this been as its approppriate. Having been through the process of putting p gasket on, taking water pump off, replacing gasket, still leaking and now having fitted a new pump, I can't get any heat out of the heater. Doesnt seem to leak, although I had the brainstorm of opening the plastic plug on top of the thermostat housing to try and bleed the air out, I got a whoosh of coolant all over me and the plug flew off. Managed to find it and put it back. Next I left the engine running with the expansion cap off for 10 mins. Still cold. I might have to see if Busterbus wants to sell his dodgy electrical heater!