i noticed there is a small copper pipe that is disconnected from the fitting on the main pipe on top of the water heater and I am unsure of its purpose. I had a family relative remodel our laundry room 2.5 years ago and he made a lot of mistakes with the plumbing. I am wondering if he forgot to reconnect the line or it was always this way. What is the purpose and do you recommend I reconnect it or leave it disconnected?