My kitchen pull-out faucet vibrates when turned on full. Sound like a filter that needs cleaning? Also seems like the pressure/flow is diminished a bit.

Following link has troubleshoot walk-thru:
http://waterheatertimer.org/Low-water-pressure.html

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I had the same issue with an American Standard faucet that I installed new 6 months ago. The diverter can be the issue if you have a sprayer attachment. Try unscrewing the sprayer head from the hose it's attached to. Now run the water full pressure with the hose pointed into the sink, obviously :~). After running the water for about 1 minute, connect the sprayer head back onto the hose, make certain the flat rubber washer and ring gaskets are seated in their grooves properly, and tighten until you have no water leaking from the sprayer head/hose connection. Now try the water through the faucet. If the problem was a temporary diverter issue, your pressure should be fine now. Good luck

1) Guesses: Sounds like a bad single-handled faucet cartridge, or low water flow at faucet, or clogged water filter.
Replace faucet cartridge, clean the aerator, and/or clean sediment out of pipes below sink, and clean water filter at tankless unit each month.

2) For exact measure of problem:
Typical faucet can have 2 gallon per minute flow rate.
2 gpm flow rate means faucet fills 1 gallon container in 30 seconds. Test faucet using 1 gallon container and a cooking timer to get flow rate.
Clean aerator to improve flow rate. Compare kitchen flow rate with other faucets in home.
http://waterheatertimer.org/Low-hot-water-pressure.html

Most homes have 1/2" diameter pipe running to kitchen faucet.
100 feet of 1/2" diameter pipe holds 1.2 gallons of water. This assumes no sediment build-up inside pipes.
http://waterheatertimer.org/Water-heater-recirculation-system.html

Assuming only hot is turned on: If faucet is 100 feet away from water heater, and pipe diameter is unobstructed 1/2" diameter, and faucet has 2 gallon per minute water flow, then hot water should arrive in 36 seconds.
50 feet away, and hot water should arrive in 18 seconds.

If kitchen has single handled faucet, and the handle is raised in the middle, then equal amounts of hot and cold water are drawn at same time. This doubles amount of time for hot water to arrive.

If single handle faucet has a bad cartridge, then faucet can have crossover.
Crossover means that cold water can enter the faucet even if faucet is turned to hot.
Bad single-handled faucet cartridge can delay or stop the arrival of hot water.
http://waterheatertimer.org/Crossover.html

Tankless require maintenance including cleaning combustion parts yearly, de-lime heat exchanger frequently, and clean water filter each month.
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf
http://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

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don't believe the ball is the problem,is there a screen on the end of the flexible hose where it connects to the spray handle,theres a screen someplace

Could be a blockage in the valves and check any filters any where in line.some sinks in kitchen have a filter under sink and check valve to make sure they are opened all the way.

yes it should have a flow restrictor in the end of the spout. You might need to clean it out

To get full pressure you need to pull the wand away from the base. Then remove the wand from the hose becareful not to loose the washer. When the wand is removed look down the wand you will see a plastic part. That plastic part is a flow restrict-er. You need to put a screw in the restrict-er and pull it out. When it is out put wand back on the hose then you will have full water pressure.

Check the screen at the hose connection under the sink. Check the hoses for any large debris in them. Verify that the water pressure coming from the water outlets under the sink is good. There is obviously a restriction somewhere...you just need to locate it.

Sounds like the cartridge needs to be cleaned or replaced. May be clogged or faulty. This requires turning off water under the sink and pretty much taking the faucet apart.

Your problem is a simple one.

1. Turn off water to faucet.
2. Place a towel(s) in the base of the sink(s) to prevent any parts from going down drain.
   
3. Remove the handle to the faucet. (single handle only)
   
4. If not a single handle then remove spout from faucet.
5. If a single handle remove cap carefully and any loose parts.
6. Gently turn spout side to side while lifting to remove.
7. You will see a hole with a very small valve where the water comes out to the spout on the base of the faucet.

1. Remove this valve (which is a backflow preventer) and replace.
2. Reassemble and test.
   

Problem solved.