We had 17F at night, I let warm and cold water on dripping. But this morning the hot water wasn't running in the whole house.
I opened all the hot water faucets, when I turn on cold water there is water coming out of the warm water faucet, but it's cold. Are they somehow connected? Why is the water coming out of the hot water faucet only when the cold one is running.
Oh maybe I should mention that I will run cold water upstairs with the hot water turned on, and the water will run downstairs in the kitchen sink and toilet out of the hot water, but only when the cold water upstairs is turned on and vice a versa.

Well I know what happened.
The cold water pipe going to the heater froze on the outside wall, so did the washer pipes.
The cold water that was coming out of the hot water tap, was due to the pressure (I think)
As soon as it got to 37F and all the hot water taps were open, it made a loud noise and water started running out of all the taps. I checked for leaks and didn't find anything, not even outside. I hope the pipe is all right. The noise was the air pressure in the pipe.