Hi,
Here a quote from this link:
Fuel
Leaving a fuel pump on with a low pressure light illuminated is not only an explosion risk (see Thai and Philippine write offs) but also if a pump is left running dry for over approx 10 minutes it will lose all the fuel required for priming which will render it inoperative even when the tank is refuelled. If you switch on the centre tank pumps and the LP lights remain illuminated for more than 19 seconds then this is probably what has happened. The pumps should be switched off and considered inop until they can be re-primed.