I installed Series 26 Avalon faucet. The water flow rate is very slow. All fittings to the faucet are new. Could the problem be a faulty valve ?

The specs say that there are two check valves but the diagram does not show them. Take the weight off the hose and see if it is causing the restriction. If it is not, what is the water pressure in the house? The 2.2 GPM is the maximum flow rate.

Check the supply line and valve to see if any dirt or foreign.matter got into the line or valve when you changed out your faucet. if this is not the problem you may have a faulty faucet. You may be able to back flush the faucet with a garden hose by leaving the hot side open, but you will get wet. If you used Teflon tape on the supply line and it is a compression fitting, some of the tape could be blocking the water. for more info go to waterheaterflush.com

Before calling service technician, open following link for Rheem troubleshooting resources.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

List of causes MIGHT include one of following:
Bad household circuit breaker that powers electronics, or loose wire inside outlet where tankless plugs in.
Tankless fuses and control board.
Water flow rate too low. Minimum .8 gallon required (depending on model)
Tankless inlet filter clogged.
Household aerators clogged at faucets.
Crossover at single-handled faucet
If installed, there can be crossover at mixing valve.
Faulty household check valve, including check valve on re-circulation system if that system is installed.
Restriction in household water line, such as clog at elbow.
Unequal pressure in household hot and cold lines, caused by restriction in hot line. When single-handled faucet turns on, the cold water pressure is higher so hot does not flow and tankless will not turn on.
Loose wire connection inside tankless.
Unit temperature set too high.
Unit temperature set too low.
Water temperature is very hot coming out of tap, so more cold is added, but that reduces amount of hot water flow, so tankless turns off because flow rate is too low.
On some tankless, if water is preheated by solar or other indirect source, the burner will not activate.
High mineral content in water > delime tankless yearly
Misaligned temperature sensor
Low gas pressure. Wrong type of gas. Undersized gas line.
Too many faucets on at same time.
Faulty tankless water valve. Water valve stuck.
Fluctuating household water pressure, for example MUD and PUD district water pressure problems or water well pressure.
Faulty household pressure reducing/regulating valve if installed.
Faulty household pressure tank, if installed -or- pressure tank needs to be installed.

If flow is slow to shower,pull showerhead,small watersaver hole and screen have garbage in it,teflon tape-rust sand etc Tub spout working fine?

Might be a bad inlet valve. To confirm, swap the hot and cold hoses to your washer so that the cold water feeds the hot water connection and the hot water feeds the cold water connection. Turn off both hot and cold water faucets. Set the washer for a warm water wash. Turn on the cold water faucet, and check the flow. Then turn off the cold water faucet, and turn on the hot water faucet and check the flow. If the cold water flow fill slowly, then the problem is with the inlet valve.

It an easy part to obtain from an appliance supply house. To install disconnect the hoses to the back of the machine, and remove the back panel to get access to the valve. Should only take a couple of minutes to remove and install. Hope this helps you.

You need to clean your aerator is the most likely cause for the low water pressure after the installation of the new faucet.

The faucet was installed upside down.
The shower riser pipe in the wall is to short( the distance between the faucet and shower head).
One of the biggest problems is if your shower faucet was installed with Pex pipe to the tub spout. Pex pipe will restrict the flow and force the water back up and out of the shower head.
The tub spout must be piped with at least 1/2 brass pipe nipples and fittings, or 5/8 OD. copper pipe and fittings.
Hope this helps, if you further questions please let us know.

'DO NOT REMOVE"! lol JUST KIDDING. >You may need to remove again to find out why the valve seat is not sealing In fact, expect that you will. The grit is white in color? did you see any special washers or seals in the DNR zone? wHEN REINSTALLING THE VALE BODY, YHE STEM SHOULD BE ALL THE WAY OPEN . cLOSE THE VALVE ONLY AFTER ALL IS IN PLACE. AND YOU NEED An INLINE STRAINER IN YOUR WATER SYSTEM.. gOOD lUCK _nED_

sounds like your diverter is stuck or improperly installed ,try tapping at diverter location to free up diverter the other thing to try is remove the little device on the end of spout make sure its not clogged with debri

Start by removing the spray head from the hose. Pull the spray head out and with a channel lock pliers unthread connection between the spray head and hose. BE CAREFUL not to let the hose fall back down into the faucet. With the hose directed down toward the sink test for volume by turning on the faucet. If you get a nice volume the problem is in the spray head. This is usually the case. Put the spray head back on then remove the aerator. It's the screen where the water comes out of the spray head. Clean out the assembly ( 3-4 parts). Reassemble and test.

Good luck, Phil