I have Discovery 2 (2000) with Td5 engine. acceleration was lumpy so changed the filter (overdue) and although initially it started it stopped right away and won't start. I have followed recommendation (switch on 30 sec, switchoff 15 etc) but still no joy. The pump is silent and the new filter is empty. There is power to the filter. Q: Would an air blockage between the pump and filter cause it to stop or is the pump broken ?