Very cold in Ohio... 25 below... had cold water but no hot water... defrosted hot water line from attic to tank... have hot water in kitchen but no hot water in bathroom. Have the shower valve for hot water open and when I turn on the cold water in the hand sink, water comes out of the faucet in the tub. I turn off the hand sink and the water stops flowing in tub. Ranch style home. What can I do to get hot water to shower?