Fuel Gauge Stuck On Mondeo Diesel 2002

[Greenfaldo]

Afternoon people.

Just bought a 2002 Mondeo Zetec 130.

Looked at the car fuel light was on and needle was very low, when i picked the car up they had put some diesl in and the light had gone off but needle was still down, filled up tank to the rim but light stayed on and needle was still down, spoke to a dealer and they said maybe it'll take time for the sensor to kick in and reset. After 3-4 miles light went off and needle raised a little. This morning the light went out normal and the needle has raised to inbetween 1/2 and 3/4.

Could it be that the thing inside the tank has got stuck but it'll move itself? or could it be something else.

Thanks