I am not a plumber so please bare with me because I don't know the proper terms. I have been dealing with a very complex issue that numerous plumbers and managers can't fix. When I turn on the cold water, it turns very hot and after about a minute, turns back cold. I have put in a new hot water heater and new shower valves and nothing changed. It's not a furnace issue or piping issue according to plumbers.The house is only 7 years old and I had no problems until February. It is a townhome but all the piping is separate and nobody in my row is experiencing plumbing issues. There are some warm spots on the floor but the plumbers don't think its a slab issue. There is no basement. sI don't want to pay for all thee plumbers to come look at the issue, charge me, and then say sorry, can't help so I thought I would see if any of you have ever dealt with this. Any help would be appreciated. Thank you.

difficult to say without being there. you have a cross connection somewhere.
but, the most common places to look are for a recirculating HW line that has a faulty check valve or a shower valve that has an internal problem.
grab the shower valve as close to the wall as you can to see if it feels hot after not being used for a number of hours.
also look around the water heater for a circulating pump. also feel the pipes around the heater to see ifthe hot outlet pipe is always hot to the touch.

Plumbers don't THINK it is a slab leak? They either KNOW or don't, but what you describe DOES sound like a slab leak. You may need better plumbers.

If you have copper tubing rolled under your slab it is probably a leak near that hot spot on the floor. I would install PEX if you have an attic. Eliminate copper entirely.