This can be hard to find. I did a hotel and parts of it complained about no hot water. It took three days and two different plumbers to find what was going on. There were some valves left on in some uncompleted rooms where the shower valves hadn't had the cartridges put in yet. The mop sink was also contributing as they had a chemical mixing station hooked up to it.Yes, I have a recirculating system. What should I be checking for to identify and correct the cross-connection?
It's usually laundry, mop sink (or similar), the water heater itself where there lines tie in, or showers. These can have the hot and cold tied together and constantly on.