Gate sensors does not work when raining

[vanbinh]

Hi. I don't know anything about the gate opener. I use a Genius sliding gage about 4 years ago. It works really well, but in recent days I notice the receiver sensor has a problem when it rains (the sensors do not pick up the signal but when the sun shines another day it works again). When I turn off the power and turn it on again the red light (two dots) flash then stop. It is supposed to be steady. Please help me to see what caused this problem (the sensors or something in the board?). I ask a man to repair it but he advice me to replace the whole that includes the monitor (while it still working well).