Hot Water heater has low temp water

We have a state brand gas water heater which was installed in 1997.

I replaced a defective pressure reducing valve on my water main coming into my house a few days ago. Since then, my water heater only produces luke warm water. WHen I turn the water heater thermostat up to a higher temp, the gas ignites as it always has, heats the water a bit, but that's all.

We have a gas range and have sufficient gas pressure there ot not notice any difference it performance when we cook.

Any suggestions about repairing or replacing this unit?

It`s possible that the dip tube is broke off. It is 11yrs old and nearing the
end of it`s life span,You may save yourself a lot grief if went ahead and
replace it.

State is not known as one of the higher quality WH...11-years is pretty good. The process of opening the gas line and doing maintenance could have dislodged some debris - it may have gotten to the WH, but not the stove. It could be partially obstructing the WH gas valve, but it should still reach temp, but could be slower or not as efficient.

You could check the dip tube and replace it if it is broken. This would buy you a little more use from the heater, but as others have said, this heater is at least close needing replacement. The dip tube is located in the cold water intake. It is flared and just hangs under the nipple. Fish it out with your finger. It should go all the way to the bottom of the tank. If it is broken just buy a new one (less than $10) Trim it off if necessary. The dip tube injects the cold water into the bottom of the tank where it is heated. The hot water rises in the tank and you use the water from the top of the tank. If the tube is broken, the incoming cold water mixes with the warm water at the top of the tank so you just get warmish water. State heaters are not considered to be very good quality, so when you do replace it, you might consider a Rheem or Bradford White. The Bradford White is usually sold only to professional plumbers.

On a lot of the 11 year old water heaters I see...
If you undo the cold supply you might as well keep undoing connections!
Then slide that new one in place!

I think you are saying that the water doesn't get as hot now as it did prior to replacing the PRV. If you replaced that to get higher pressure (more water flow) that means that now the water is not staying in the water heater as long as it was before; it moves through it faster. So it can't get as hot as it did. A bad dip tube is a possibility but more likely it is hard water scale build up in the heater. Any scale has to be heated before water can be heated and scale displaces water, so there is less water in a scaled up tank.

Do you have hard water?

Do you have a water softener? If yes, has it always consistently given you 0 gpg soft water?