Clare Snyder writes:

On Wed, 30 Jan 2019 12:38:35 -0800 (PST), Davej
wrote:

On Wednesday, January 30, 2019 at 1:17:35 PM UTC-6, micky wrote:
In alt.home.repair, on 30 Jan 2019 09:42:38 -0800 (PST), 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?

You think your pipe is frozen?

How close is quite close to an exterior wall?

How cold is it in your house?

You seem to think the frozen spot is upstairs. Maybe it's downstairs.
How many holes will you make?

Both the hot and cold water won't run?

If you have other sinks, and I can tell you do, why not wait until
things warm up. Maybe you'll have water then, with no effort on your
part and no hole.

Apparently two pipes are frozen 19 and 22 inches to the inside of the
exterior wall, or so it seems looking at the basement view. The pipes
run up in an interior wall which connects to the exterior wall near
the front door. The house thermostat was set to nighttime temps of
55F upstairs and 60F downstairs. I have two shutoff valves at the
points where the copper pipes head upward in the basement. I've only
lived here 1 1/2 years so this is the coldest I've seen it here. No
other faucets seem to be in trouble.

I think I can rent a fancy thermal camera at Home Depot, but what
would it really tell me?

My thought is that with a few inspection holes maybe I will discover
why I apparently have an insulation problem of some sort.

Turn off the shutoff valves NOW (and leave the taps upstairs open)
and wait for the temperature to come up. With any luck the pipes won't
split. Regardless, if they will split that damage is already done.
Once the weater warms up stuff that outer section of wall with
insulation right out to the external wall and check for anything that
would allow cold air in. Block any holes

That last advice helped me this year.
Last year hot and cold froze in a bathroom with inside walls.

Had me confused for a while, then I remembered the eaves that
led from an unheated garage to right under the bath room.
I turned on the exhaust fan in the bathroom underneath and
the pipes unfroze in minutes.

This summer, I crawled in there and first thing I noticed was that the
insulation had fallen away from a hole made to accommodate
the exhaust fan. Sprayed some foam to seal the opening and so far,
even with a few days of extreme cold, no frozen pipes.

I also had another exhaust fan let in rain this year.
Took a look at the fan vent and a couple of vans had gotten
wedged open.

--
Dan Espen