Having trouble with the rate controller in my sprayer. It works in manual mode but when I switch over to rate control mode it works for a while and then quits. Pressure drops until nothing comes out of the nozzles. If I switch back to manual mode, it starts working again and keeps going until I switch back to the rate control mode. Pressure, flow rate and mph look good when I am in manual mode which leads me to think the sensors are okay. I should mention today is the first day I have used the sprayer this spring. It worked fine last fall when I put it away. Any suggestions on what I should check before calling the dealer?