On Wednesday, January 30, 2019 at 12:42:42 PM UTC-5, Davej wrote:
No water in one of the upstairs bathrooms this morning. Thinking of
cutting a hole in the wall to try to figure out where the coldest
area is. In the basement I can see where the pipes go up. It is an
interior wall but quite close to the exterior wall. Any suggestions?

Depending on how desperate you are and how much you're willing to spend,
you can call local welders. They can hook up an arc welding rig to pump
current through the pipes by attaching a cable to each end where accessible,
which slowly warm the pipes. That is if they are metal. I guess you could
DIY, but that would require buying some arc welding gear.