It could be that you lost power to your controller and the rain sensor needs to be re addressed. If you remove the outdoor portion of the sensor and take it to your controller. Hold down the small spindle on the top of the device for 5 seconds and then release it, it should recognize it and start to function once again.

All Wet
Texas Licensed Irrigator #1897 since 1984

all wet is all wrong. if the sensor is reading red (wet) because of a power outage.......the system will not come on. DO NOT bring the sensor within 5 ft. instead, go to where the sensor is installed and hold the pin down for 5 seconds. if the light turns green you are all set. hunter designed this sensor so that when it installed, in order to activate it you must hold the little pin down WHERE IT IS INSTALLED to confirm a signal between the sensor and the receiver. if it is a few feet away of course it will work. but if it is somewhere else it may not be transmitting a signal. so keep it where it is and test it. if it doesnt turn the red light green.......move it to another spot and test it again until you get the green light. remember everytime you lose power you need to reset it by holding down the pin. ive installed hundreds of these. so try my method please.