We have a 1923 home that has been totally replumbed about 10 years ago. Recently, we had a plumber install a sumpjet and we noticed the water pressure go down some after that installation, especially on the 3rd floor. This morning, the cold water on the
3rd floor bathroom sink worked just fine about 6am. A couple hours later, there was no cold water coming out of the faucet. Since then, I can not get any cold water to come out only on the 3rd floor and only with the sink. The bathroom sink on the 3rd floor was a faucet in the middle with hot and cold handles on each side. The hot water works just fine, it is only the cold water that does not flow. The toilet on this floor and the shower work just fine. The cold water in the 2nd floor bathroom sink as works just fine. I can not find any leaks on any floor. What could be the problem that the cold water no long flows on the 3rd floor.
Thank you,

I also forgot to add that this week, the temperatures have dropped into the teens (f) at night. The pipes are wrapped and the outside water has been turned off, faucets wrapped.