I have several of these and all of a sudden the sensor at the bottom of the handle on 4 of them have become patchy you can see the orange light come on as you lower the handle then there are dead spots where it goes out and then on in again as you pull the handle down. could this be dirt as they are used outside, or cold its unusually cold here just now. and can i clean it myself if it is just dirt. Any Help is appreciated thank you.