Unfreeze Bathroom Pipes ~ Bethany Find Decor

Unfreeze Bathroom Pipes

Big freeze, new house. Just found out the add-on bathroom was plumbed by amateurs, and the cold water supply froze. I don't have access to the frozen section of pipe (without major demo), so I can't heat the pipe directly.

If I open the hot and cold tap on the sink faucet at the same time, while also opening the cold tap on the tub in an adjacent bathroom (which is also affected by the frozen pipe). The hot water backflows through the diverter of the faucet, and comes out in the tub. I'm using this backflow technique to try and heat the pipe enough to hopefully, break up the ice in the pipe.

All this got me wondering. If I have a plumber come out, is there anything they can do? Do they have a special tool or technique to deal with this situation? Would the plumber simply want to start cutting holes in the walls/ceiling to gain access to the pipe?

More info:

The water supply for the second bathroom seems to be tapped off the tub supply lines of the original bathroom. In the original bathroom the sink and toilet work, but the cold supply for the tub does not. This means that the frozen section of pipe is after the sink in the original bathroom, but before the tub in the same bathroom.

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^{Rough sketch of cold water plumbing}