peugeot 406 fuel gauge sticking?

hi there, ive got a peugeot 406 1.8 petrol its 2002.
ive only had for 2 weeks, i bought it off my brother in law. its been on his drive for 4 years,
unable to use due to ill health. its only done 37000 miles. im having a problem with fuel gauge,
when its low on fuel i put some in but the gauge does not go up?? after about a few hours it goes up to the right level, and i have the same problem
when its low again???
could this be the float sticking? or could this be something else??
if anyone could help this would be great.
thanks for your time. andrew.