I recently bought an old Victorian. There's a half bath on the first floor which was an addition before me.

After 3 days or so off a deep freeze in the NE where I live. The water stopped flowing into the half bath. I surmise that it had frozen somewhere since when it warmed up a bit the water started up again.

Since the bath is well inside the house, I have no idea where it cold be freezing.

Any ideas on how to prevent the freezing?

I know that eventually I have to crawl around the house and find the place where it needs insulation. But I'm not keen on doing that when it's 10 degrees out. Any backup ideas?