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We have running water on the main level..
That does not help.
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I have house heat cranked
That may help some.
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and a space heater in the bathroom.
That probably helps
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Faucets are set in the on position.
That is good.
The pipes for the upstairs bath must be in an exterior wall somewhere. Where is something only you could try to determine. That is where you would want to provide additional heat. If the bath is arranged such that the pipes could be in a wall behind a cabinet, open the cabinet and provide heat to cabinet.
If you can turn off water to the branch lines that supply that bath, suggest that you do so, in case a pipe has burst. Otherwise be alert for leak when pipes thaw.
Temperatures are a bit low but not all that unusual. Suggest that at some convenient time you open up the wall these pipes are in and take steps to prevent freezing. Sooner or later they will burst.
