99% of the time we remove the four screws from the top of the solenoid and remove diaphragm. There are two small holes opposite of each other in the diaphragm that allow water pressure to get to the opposite side and seat it to stop the flow of water. These holes get a calcium build up. There is a spring that you need to be careful not to lose and make sure to get back I place. Usually takes about 20 mins if I get phone calls while doing it!