Replace the solenoids. they are a constant problem with these units. Usually easy to find through dealers or repair agents may have 2nd hand units that once tested, will work OK for quite some time. Easy to change. Copy the wiring to a sheet of paper before changeout. Remember to turn off the juice and pull the plug before openeing the small panel at the back for acess.
Best of luck
Jeff
Jeff Howell, June 2005