[Darrel1]

We are refurbishing a master bathroom, and are having a problem. We have torn out a tub in one area, to be replaced with a walk-in shower, and we are replacing a sink-vanity in another area of the bedroom with a whirlpool tub. The areas are near each other. After the work begun, I have lukewarm water at every faucet and shower in my home. However, the water heater is only about one year old and seems to work very well. I have two single-lever faucets in showers - one is new, on a recently refurbished main bathroom. The second is approximately thirty years old, the same age as the house, and is for the torn-out tub that will become a walk-in shower. A plumber recently roughed out a Delta R4707 Deck Mount Roman Tub with Hand Held Diverter for the whirlpool bath. It is not completely installed yet. We are going to have the tub tiled.

I have done several checks:
1. I checked the water drain at the water heater - the water is very hot. I turned the thermostat a bit above the recommended 120 degrees.
2. I turned off the valve from the line leading into the water heater and I still get abundant cold water flow from every faucet in the house.
3. With the valve leading into the water heater open, I get lukewarm, variable-temperature flow from every hot-water tap in the house.
4. With the valve leading into the water heater open, I opened the hot water tap on the sink. The hot-water line leading from the water heater along the basement ceiling grows very hot along its length until it reaches a "T" connection that goes somewhere upstairs. After the "T" connection, it is warm, but much cooler than the line before the "T". The side opposite the "T" runs towards a utility sink in the basement.
5. I have opened the hot-water tap in the kitchen sink with the water lines to each of the washing machine and the dishwasher turned off, and I see no improvement.
5. I have opened the cold-water tap in the kitchen sink, and it starts cold and gets a little warmer if I let it run for awhile, but not as warm as the hot side.
6. We will be removing the older single-lever faucet, so we can cut it out of the system and cap the lines off. We will install a new single-lever faucet in the new shower. The older faucet is near (about ten to twelve feet) from the newly-roughed-out Delta faucet. I do not have valves to separate either the old lever faucet or the new single-lever faucet from the system.
7. We did not have this problem when we installed the new single-lever faucet in the other bathroom.

I have two suspicions: either the new Delta faucet has a cross flow, or there is a cross flow in the older single-lever faucet. The new single-lever faucet could have a cross flow, but I would suspect the old one first. The Delta faucet has corrugated lines from each valve to a "T" that leads to a diverter. The diverter will divert water to a sprayer when the assembly is complete.

Is there any way to rule-out the Delta faucet before we tile and enclose the faucet? There is no valve in the line to the faucet area. Any other places to look? The plumber did cut some lines and run the lines further to relocate the Delta faucet from where the old vanity sink was, but I do not see anything crossed. Could the work have caused debris to lodge in the nearby older faucet?

Thanks!

[Darrel1]

It did turn out to be the new faucet. The stem assemblies were installed 180 degrees out of phase, so that water flowed through the diverter portion. I rotated the stems and the water is hot again. Thanks to anyone who took time to consider this post.

[KISS]

I just did and that's what I would have suggested.
Thanks for the update.