If the problem isn't with the glow plug control relay then It could be the engine temperature sensor, if you check the wiring diagram for your model in your haynes manual it will show you if the glow plug circuit is temperature dependent. The sensor is quite easy to replace yourself, I think it is in the thermostat housing. The other thing to check is if you have air in the fuel system, a leaking pipe will let air into the system and even tiny bubbles will prevent it from starting. Try tow starting your car, if it starts after a tow then continues to start whilst it's warm, it's probably the sensor, if it starts but dosn't continue to start when it's warm, there may be air in your fuel system, so then you'd prime the system (after repairin the leak). You can flood these engines when priming so then a tow again can be enough to get you going.
Jullie, October 2008