Thanks for all your responses. We went back over there yesterday and checked the water meter. The dial was spinning even after we made sure everything was shut off. Then we shut off the supply valve to the water heater and the water meter quit spinning. We left the valve off for a while and when we did turn it on there was hot water. This tells me there is an under slab leak in the hot water pipe.
We used an inferred thermometer to test the temperature of the floor near the kitchen sink and in the bath rooms while the water heater had pressure and when it did not have any pressure to see if there was any difference and found none. This was done over a few hours, but still no temperature difference in the floor.
Any hints on finding under slab leaks?
Thanks,
cm