Why don't I have hot water after replaceing faucet cartridge?

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

Add a comment for more help.

Take a moment and rate answer for accuracy:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Hot water side of most faucets give most problems try heating with hairdryer pryor to trying to remove,contact moen tell them of your situation they will more than likely send you a new cartridge free of charge if you raise enough stink about just replacing cartridge.

Go to delta website, take a picture of faucet with your cell phone and send. They should be able to identify and send you the parts. Meanwhile you'll have to turn water on and off from the emergency shut off valve under the sink. If it looks like the picture, it's probably the rubber seat and spring. If you don't want to wait go to your local "hardware" store. There may be someone there to help you. Bring the stem or cartridge, along with the rubber seat and spring. Don't use cold water while stem is removed. Turn cold off as well to prevent a mishap.

If you have full pressure on the cold water side and low pressure on the hot side then you well need to remove and clean or replace the cartridge for the hot side. If you have low water pressure on both sides try removing the aerator and cleaning it.
If you need to replace the cartridge on the hot side do both sides while you at it.
Whenever you work on any faucet before you turn the water on remove the aerator and run the water for a few seconds then replace the aerator.

Cartridge removal is a simple matter of exposing and pulling out the old cartridge. Before getting started, turn off both water valves underneath the sink and allow the water to run until the line is clear. Using a screwdriver, gently pry off the cap on the lever of the faucet handle to expose the cartridge. Remove the U-shaped retaining clip that holds the cartridge in place and pull the cartridge out. If dirt or residue makes removal difficult, use a Moen cartridge puller to assist you. A cartridge puller fits over the cartridge and gives you greater pulling power.

Soak the dirty cartridge in vinegar for four hours and replace.

If cleaning the cartridge does not work, call the Moen Helpline at 1-800-465-6636 or Customer Service at 1-800-465-6130 to order a free replacement. Locate the part number on the cover page of your instruction manual. If you no longer have the manual, look on the underside of the spout.

Depending on what brand of faucet you have you may need to replace the cartridge,moen and clones, or stem/cartridge on delta and similar. I would not replace the faucet until I was sure that you had hot water to the kitchen faucet and the faucet was going to cost more to repair then replace.
If you have supply valves for kitchen faucet I would shut them off and try to take faucet apart to determine where the hot water is stopping. Do not try to force things to much or you may make the faucet totally useless.
If you know what name brand your faucet is you can find several sites on u-tube that show good repair procedures.
I hope this helps you. Thank you.

Yes, debris from water heater replacements often breaks lose and gets stuck. The problem could potentially be anywhere between water heater and the faucet. The faucets shut off valves or the Delta faucet cartridge itself. Turn the hot and cold water valves off under the sink and disconnect the water supply lines from the faucet. aim the water supply lines into a bucket and turn the valves on one at a time. If there is a significant reduction in the water pressure and volume on the hot water side, you need to replace the shut off valve. If there is no reduction in water pressure, you need to clean and/or replace the Delta faucet cartridge. Contact Delta to receive free replacement parts.

Hot water line connected to left side of faucet? Did you replace tap set, or just cartridge? Cartridge may be out 180 degrees.

The faucet cartridge is more then likely blocked and the faucet will have to be disassembled in order to unblock it.
While it is disassembled you should slowly turn on the water lines to make sure the water ways in the faucet are clear. And thoroughly check the cartridge for damage. Replace if necessary.
Replacement Cartridges can be purchased at most plumbing supply houses or Big Box Stores such as Lowes or the like.