A faucet's diverter valve operates to shift the flow of water from the spout of the faucet to some other exit point, typically a sink sprayer. A loss of water pressure is symptomatic of a defective diverter valve, as the valve can become dirty or corroded. Sometimes simply cleaning the diverter valve can remedy the problem. However, more extreme cases require that the diverter valve be replaced, particularly if the valve's seals have cracked. The Moen Company is one of the largest faucet manufacturers, making replacement diverter valves readily available.
Turn off the water supply at the shutoff valves or at the main water supply, which is usually located at the water meter. Then loosen the set screw located at the base of the faucet's handle with an Allen wrench. The set screw is used to hold the handle in place. Lift the faucet's handle up and away from the faucet.
Remove the faucet cap. The faucet cap is located just underneath the handle and resembles a cone. Note that the sides of the cap are ribbed. Wrap the jaws of the pair of adjustable pliers with tape to avoid scratching the finish, then grasp the ribbed portion of the cap with the pliers and turn the cap in a counterclockwise direction until the cap is loose. Lift the cap away from the faucet assembly.
Remove the plastic faucet cam, rubber cam washer and the metal rotating ball from the center of the faucet assembly. These components only sit within the assembly and can therefore simply be lifted out. Remove the faucet's spout to reveal the diverter valve by lifting it upward.
Remove the diverter valve by grasping the valve with a pair of needle nose pliers and pulling the valve out of the faucet. Pull the hose at the back of the valve away from the valve to remove it. Slide the diverter valve's hose over the back of the new diverter valve, then slide the new valve into place.
Slide the faucet's spout over the faucet assembly. Insert the metal rotating ball into the center of the faucet assembly, followed by the rubber cam washer and the plastic faucet cam.
Position the faucet cap over the center of the faucet assembly and tighten the cap into place with the adjustable pliers. Place the faucet's handle over the assembly and tighten the set screw on the side of the handle with an Allen wrench.
Turn the water supply back on to complete the replacement process.