The most common cause is mineral deposits in the sprayer. Remove and soak it in a 50/50 vinegar and water solution for several hours. The second most common cause is a kinked hose under the sink. Check to be sure the hose doesn't kink when the sprayer is pulled out to be used. Third, the problem may be a blocked or damaged diverter assembly. Follow these steps to solve:

To access the diverter -- Single-handle faucet:

1. Shut off water supply under the sink.
2. Cover drain opening so parts won’t fall into it.
3. Remove the handle, cap, cam, packing and ball assembly.
4. Gently rotate and lift off the spout.
   
5. Remove the diverter assembly. Be sure to remove the entire diverter.
   
6. Insert a flat head screwdriver or an Allen wrench into the body cavity to pop out the diverter. Check for debris on the diverter, as well as in the diverter cavity in the faucet body.
7. Clean the diverter thoroughly by soaking in a 50/50 vinegar and water solution for two hours; reinstall. If diverter appears damaged, replace it with Delta® diverter RP320.

To access the diverter -- Two-handle faucet:

1. Shut off water supply under the sink.
2. Cover drain opening so parts won't fall into it.
3. Unscrew and remove the spout nut. Use a crescent wrench to loosen if necessary.
   
4. Unscrew the diverter from the top of the body using a coin
   
   (if the diverter is plastic) or a screwdriver (if the diverter is metal). Be sure to remove the entire diverter.
5. Clean the diverter by soaking in a 50/50 vinegar and water solution for 2 hours. Flush any debris from the opening.
6. Replace the diverter and spout nut.
   
   Check to see if the diverter functions properly. If not, replace it with Delta diverter RP6073. Be sure that the old diverter gasket is removed from the diverter cavity. The new diverter may not operate correctly if the old gasket is not removed.

Be careful not to over tighten the diverter.

NOTE: Old style metal and current-style plastic diverters are interchangeable.