Help! Frozen hot water pipe in my main bath!

[Michael Stole]

It was -22 F in the last couple of days in Ottawa, and yesterday morning I suddenly got no hot water in my main bath. Because this is an old house built in 1939, I suspect that the hot water pipe comes to the bathroom through an exterior wall, and there is no insulation there.

Now I got two different opinions from my two contractors. One says there should be no crack since it was extremely cold for only two days. He suggests to wait for a couple days after the temperature comes up, and the hot water will come back itself. In the future when it is cold like this, I just need to keep the tap dripping to keep it from frozen.

Another one says there might be cracks and I should fix this problem ASAP. He suggests to open the wall to find out where there cracks are, and then either put insulation there or move the pipes to an interior wall. If I don't fix it, when the temperature is up, I will have a leaking issue causing much more problems.

Now what are your suggestions, BPers?