Coolent light stays on but not overheating

Inside the top up tank there is a little float, I usually locate it and just work it up and down with a screwdriver, lots of times as the float can get stuck, failing this check the little sender unit under the said tank, but I must stress KEEP AN EYE ON TEMP GUAGE. This is a proper pain as I experience this often but used to it now, once a week when checking water level I just put screwdriver in and bounce the little float. hope this helps