Reversed hot water flow?

I had some work done in my basement yesterday (plumbing for a new bath.) When I got home to check it out there was hot water in all my cold lines and vice versa. I ran the cold lines for awhile and it seemed like it got the cold water in the right lines.

Now I am not getting hot water, I get about 5 min of warm water. The water heater is 12 trs. old but it seems strange that it may have died on the same day this happened just out of coincidence.

How can the water circuit get reversed like it was? Would this mess up my water heater?

It's not difficult to get confused when plumbing. I'd definitely have the guy come back and straighten it out. You can check yourself just for your own peace of mind. The cold water should be flowing INTO the cold side of the hotwater heater... hot should go out the H side. It should be marked on top of the tank near the fittings ...H on one and C on the other. Simple test is to run the hot water and feel the pipes then look for the H or C. I've actually had one to run backwards when a mixer would be left open and valve was put on the hose pipe bibb. (at a tub for bathing dogs). Too, it doesn't sound like it..but a little warm then cold sounds like one element is out in a hot water heater.

check valve

if you look over everything and you have not screwed up
the lines, you might need to put a spring loaded check valve
on the cold incomming line going into the water heater...

we recently had one where the toilet was getting hot water
and it for some reason was doing the same thing

water

What did he do for you? If he installed a tub or shower valve, he might have left it open to test for leaks and the cold water is bypassing into the hot water side.

It won't "mess up" anything but you need to get it fixed.