Hey searched, but no definitive answer.

Bike is brand new so will probably pop into the stealer, but thought i'd ask incase there's an easy solution.
Have shook the tank etc to try and free the float, but to no avail. 

Does anyone have any ideas? Could it be the sensor? The speedo light itself? 

Mine takes about 10 to 15 seconds to go off, I haven't had any issues but I'm always a little wary after a fill.

brand new? tell the shop to fix the thing...

Seems to have gone out again now... Float must have been stuck - hopefully it will come back on when the tank is low, will keep an eye on the 100km trip for now haha.

Dont trust the light.

Take some spare fuel, go for a ride and see how far you can go before she shows signs of low fuel.
Refuel off your trip meter.

My light comes on about 160 ks but refuel anywhere between 200 and 250 ks city riding (17lr tank).
I know shes getting low when I take off at the lights and lose power due to the fuel surge within the tank.