why will my fiesta 1.8D not start without a push?

Get the battery tested, most fast-fit type places will do this free. It needs to be tested under load, not just a static voltage test.
Dont buy a battery off them without checking around for prices, and buy a good heavy duty battery, diesels need a lot of power to start, especially when it's cold enough to need the heater plugs.

fred
November 2009

have you checked engine earth lead for good clean connections,is battery correct amp/hour for your vehicle, also are you using correct grade of engine oil-if too thick will be more difficult for starter to turn engine. hope these can help you to sort it.

k
November 2009