I recently enclosed my carport and made it into an apartment. We decided to run both sides of the house off the same water heater. We have hot water in the apartment and the other side of the house as well. The problem is the cold water going into the addition the apartment I mean. The cold water comes out warm goes to cool then back to tepid. I turned off the hot water to the water heater on both sides and I was able to get cold water to the apartment. What should I do to fix this. I had a real plumber fix this up for us. I have called him but you know how it is he is busy.

Do all fixtures in the apartment have this same warm, cool, tepid condition? If you leave the apartment hot only faucet on for a long time does it ever get really hot?

Didn't you accidentally cross hot and cold water pipes during remodel ?