Here are the facts.
Our upstairs bathroom is the only plumbing we have in the upper level. Kitchen and half bath on lower floor and laundry tub and washer taps in basement. So, one hot copper 1/2 pipe goes upstairs through the exterior wall and the hot line goes through an interior wall, near the exterior wall.
We have gone away for the last two years for a week or two during the winter, and turned the heat down to around 60 F while we were gone with no freezing problems.
In late November/early December (when it really wasn't all that cold) I turned on the cold water tap in upstairs bathroom sink, and no water. Turned it off. Tried hot tap, all is fine. Then tried the tub - hot and cold - all is fine. A minute later the cold water sink tap was flowing again. Like it had never stopped. Thought that the tap might be going bad, even though I never saw it happen like that before.
No problems since then.
Yesterday, the cold stopped flowing and I started looking for a replacement faucet set. This morning, the cold still doesn't flow but the hot doesn't either. And now the toilet supply has stopped as well. But the tub still works fine. It was -2F last night and I thought that maybe a partial freeze could be the issue. I have had the heat jacked up all morning but still no change. Tried turning off the main - draining all lines by opening all taps and turning main back on. No change.
Could there be any another explanation for this kind of problem other than freezing?
Someone with years and years of experience may be able to supply some wisdom from something he or she has seen in the past. Please tell me what you think.
It's only speculation without knowing exactly how the piping system is routed and connected together. I would start by making sure the aerator on the faucet is not plugged with debris. If the aerator is plugged, the same debris is plugging the fill valve on the toilet.
If that doesn't lead anywhere, unhook a supply hose from under the faucet to see if there is water pressure to the line. If not, it's time to start looking for the frozen pipes.