TD4 Fuel Pump Problem??

HI All,
I've got an intermittent problem with my 2003 TD4 and could do with some advice if anyone has had a similar problem.
Several times now, the car has failed to start. I've not heard the whirring noise from the back of the rear wheel passenger so I've opened the boot up and whacked the side of the car and hey presto the car starts. I've never had any problem with the car when it's running, it's never cut out on me. Recently, the whacking of the back panel has failed, yet if I leave the car and come back to it the following day, it starts first time, no problem. There is never a pattern to the failure to start (short run/long run/first thing) other than the last two times it has failed to start I've noticed it is within 24 hours of filling up (only let it get down to 1/4 full before filling up again) - maybe just coincidence.
From reading the forum, this would indicate the fuel pump is dodgy and needs replacing, but can't understand why it would work again after just being left for a few hours.

Hi
How many miles has your TD4 done? When was the fuel filter last changed?
Fairly easy job to change both

sound like the pump is on its way out

Mine was the same, it had good pressure when working, but must have been sticking. A new pump cured it.

Defo the same here, when running it would keep running, a good clout in that area would kick it into going if it wouldn't start. You'll be getting the orange management light coming back on too because of low or no fuel pressure.
New pump and filter fairly easy to change

Thanks very much for the replies and the confirmation. I'll get it changed as soon as.
Cheers