No hot water at kitchen sink
 

We built a new house over a year ago and have never had more than lukewarm water at the kitchen sink or guest bath. Haven't been able to get the plumber that installed our in slab plumbing to come back out to look at it. I also have a veggie sink in an island in the kitchen. Today I turned the veggie sink hot water on and it finally warmed up, then I turned on the hw at the big sink and in the guest bath. The water got warmer in both sinks, but slightly cooler in the veggie sink. When I turned the vs off, the other sinks immediately began to cool. Any suggestions?

Start
 

I would start by closing all the cold water valves off at each sink(underneath the counter top) in question and then running the hot water only just to see what happens.

Then go from there.

Thanks so much for the suggestion. I just tried it but it did not seem to have an effect on the hot water. When I turned the big sink on did not get any warm water, got some in both sinks when I turned on veggie sink, but did not seem to be as warm as yesterday.

Hot water heater
 

I would now focus my attention to the hot water heater.

Check it all out to be sure it's making hot water and good recovery.

How long are you leaving the hot water running ?
Where are you located ?
How far is the distance from the HW heater to the faucets ?
Do you know how they ran the pipe in the slab - was it insulated from the slab ?

Only way I know to check that is in the master bath which is right next to the water heater. Seem to have plenty of hot water there.

In the kitchen it has to run about three minutes to get even warm water. We are in Oklahoma. Would estimate it's about 50 feet to kitchen sink. Have no idea how they ran the pex in the slab or whether it's insulated.

Hot water
 

50 feet is quite a run. You say the bath next to the hot water heater gets real HOT water fast?? How HOT?? Might have to heat the water up more to get HOT water 50 feet away in the kitchen area.

Check water temperature at heater.

Yeah, I'd say it's uninsulated & that 50' buried in concrete is just sucking the heat out of it
Maybe an electric instant hot water at the kitchen is a better solution

I agree with Dave might have to look into point of use heater.

Will cost more but look at the advantage, hot water fast, use a lot less water, stress gone from waiting for hot water to arrive.