John the plumber was called out today because of a high water bill thinking there was a leak in or under the home. On arrival I did a walk around of the house and saw 2 gas tankless water heaters and 1 1/2 inch main water emergency shutoff. The customer explained that they just got the pool filler fixed maybe a month ago. I wrote an estimate for a leak detection and to replace a hose bib to properly do a pressure test. The customer signed off on both and I continued my work. I replaced the hose bib and did a pressure test with both water heaters off and there was no drop. I turned on the water heater on the side of the house with the main line and did another pressure test still no drop. I then turned on the other water heater on the other side of the house and did another pressure test and there was no drop in pressure. After all the pressure tests passed I kept it pressurized and opened up the pool filler bypass valve that was closed and it started filling right away and would not