My icemaker feedline broke. I replaced it. It originates from above the downstairs shower. After replacing the icemaker feedline I lost pressure in the shower. It is a Delta Monitor. Set to cold, I get barely more than a stream, as I advance to hot it slows to a dribble. I replaced the cartridge but was no help. While replacing the cartridge I could see that I had great pressure in the mixer. I puzzled over this for a week, then I lost pressure in the upstairs toilet. After flushing the toilet it will not fill the reservoir unless I turn on the tub water, engage the shower valve, and turn the lavatory water on. Then the toilet fill valve opens and fills the reservoir.
I do have a slow drip at the main water valve that I haven't fixed just before the inside meter(in the basement). I don't believe it's related because it is not a new development.
Wife thinks I left a valve closed to the shower(hot water line) when I replaced the icemaker line... but that wouldn't have anything to do with the upstairs toilet and I wasn't working with the hot water line when I was replacing the icemaker line..