What is the least destructive way to determine where a hot and cold line are crossed? We do not want to cut into every wall and ceiling--Please help!! Thank you!

How about some more details. One tub or shower, half the house, the toilets too, unfinished basement or crawl space, etc. It may be a matter of figuring out the least destructive way of making things work right.

What is the least destructive way to determine where a hot and cold line are crossed? We do not want to cut into every wall and ceiling--Please help!!! Thank you!!
Lab's right. We need more details. Has any work been done lately? Such as working on your pipes or changing out a faucet? Did this happen all of a sudden or has it been ongoing? In other words, what's been changed in your water system? Regards, Tom