Record lows for this area (0* last night). This morning there is no water coming out of hot water faucets. None in shower, kitchen or bathrooms. Cold water is working fine. There are 3 water lines attached to water heater: 2 feel warm and 3rd is cold. Note that heater is in the garage which air temp is about 10*F. I used a hair dryer to warm up the cold pipe but had no results. All the pipes go into the walls of the house so I don't know how I can warm them up if they are frozen. Water heater has worked fine until this deep freeze. House is built on a cement slab. Is this problem frozen pipes or the heater? HELP please.
Thank you in advance.
Regards,
Chris

A little more information please.

You say that you have 3 lines to the water heater. Do you mean that you have one line, a cold coming in to the top (usually on the right) and one line to the top, a hot coming out and then branching to two lines?
Or do you mean you have two lines coming to the top and one line coming out the side (or the top)and going down the side of the water heater. That third line would have a valve on it with a little lever.

Also you say the pipe pass through the walls of the house. Do they pass directly through the wall between the garage and the house or do they go through the back wall of the garage for some distance before entering the house.

Yes, it will be the pipes that have frozen. Obviously, the heater is working or none of the pipes would be warm.