I will give that a shot. I didn't think if it in part because we're so rarely hooked up to city water.
Well, that seemed like a good idea, but no change. No water at toilet and kitchen. I confirmed no water pressure/flow in the lines to those items.
I also checked the shower again, since it's the only outlet that still has the original two knobs for hot and cold, the sinks have newer faucets with single levers. Water is indeed coming from both hot and cold.
There is no check valve under the sink.
When the weather warms again I'll take apart as much of the wet bay plumbing as I can and see what I can see, but there's not much back there. Most of it is under the floors somewhere.
