Why did the valves stop working in a few days?

I'll assume you have hot water flow to other faucets in the house, hot water to this faucet worked previously, and cold water flows at this faucet<?>. I'll further assume you haven't experienced sub-zero temperatures.

Then;
Check supply shut off (under sink) is open. Hot supply is "usually" to your left and cold is to your right. Twist valve CCW to open.

If there are no other shut off valves between this faucet and the hot water tank, then likely there's a blockage. It could be blocked anywhere between the hot water tank, up to the inside of the kitchen faucet valve. Most likely inside the kitchen valve, as it has the smallest passageways.

Check for restrictions in the shutoff valve and the stem of the hot water side.

There is a little popper in the spout area. You need to remove the top handle and slide the spout off. The popper is in the main tube coming up. It.s a standard part at most big box hardware stores and it costs less than $10.

The way anti-scald valves work is there is a slide tube inside the faucet which requires pressure from both hot and cold or else it will cut off the flow. As for temperature adjust I do not believe there is an adjustment screw but more so there are these white plastic toothed stop rings which prevent the handle from turning 360 degrees. When your adjust the stop ring, it adjusts how much hot water is allowed to mix with the cold water. My wife likes her showers a lot hotter than I, so I gave a good allowance with the stop ring. The "adjustment screws" which you are viewing are not for adjustment of temperature, they are remote cut-off screws to stop the water entirely to change the washers in the unit if needed. SO open those all the way and leave them open. Think of them as not having to go all the way into the basement to shut off the water supply just to change a few washers.

check to if there is a loose or missing washers in shut off valves under sink .

wow... I wish you hadn't gone thru the expense of replacing the faucet... it's perfectly good... your problem was the aerator, it unscrews at the tip of the water spout and had collected too much sediment which eventually blocked water flow. Often happens quickly after your water is shut off at the main valve. Aerators cost about 50 cents...

if this is the faucet in picture, turn off water, pull out cartridge and inspect for any debris in cartridge or valve body, if not, turn on hot water to see if water is getting through valve body. May have kinked line or debris from or in angle stop line.

change the washers first if that don't work change the inserts buy all at same time and return if not needed . Thank you for useing fixya please rate me

1st Check the temperature restricting coller behind the cover under the handle. It is used to restrict the flow of hot water to stop you from being scaulded.
2nd Those set screws will control the flow. Check to ensure both sides are open the same amount of turns. If the water pressure is good turn in the cold side.

It could be one of two problems, one simple, one serious.

• Easy fix
  

1. Turn off hot water angle stop under sink to faucet.
2. Remove supply line from hot angle stop.
3. Place end of supply line in a small bucket to catch some water.
4. Turn on cold water for a couple of seconds and backflush debris from faucet.
5. Reconnect supply line.
6. Turn on angle stop and test
   

• Complex fix

If you have steel pipes you may be experiencing reduced flow due to corrosion in your pipes. Reduced hot water pressure in the kitchen faucet is usually the first sign since this is the faucet that is most used in the home.

Repiping is a job for a professional. Another symptom you may need a repipe is orange colored or rusty water.