There is a main drain that runs from the basement through the roof where it is the vent for the system. If you look at the layout of the house, the upstairs bath is most likely over the downstairs one or the kitchen. If you look on the roof, you will see a 4 inch pipe coming through the roof that should be over the upstairs bath. The sink and shower drain into that and then to the basement and out of the house. Most likely the main stack is in the wall behind the toilet.
Faucet needs repaired.
The plaming tubes are all conected.When the cold water run in kitchen the cold water at the shower become less,so with less cold water at the mix cold-hot (the balance is desterb),making the water hoter.Same if you turn on the hot in the kitchen the water will be colder in the shower.
old pipes in the sink or tub upstairs
SiNk
Is the water not hot? Or no water coming out the hot tap? not comming out at all
You need to turn it off at the base of the sink. Or depending on the problem you may need to turn it off at the water main valve.
it sometime sink if it has tu much water but yes it floats
A partial bath in a home is also sometimes called a half bath, or a 3/4 bath. A half bath has a sink and toilet, a 3/4 bath has a shower, sink, and toilet.
HOT rises COLD sinks
A blocked pipe. The water can not go down the pipe, so it comes out in your sink.
There is a clog between the sink and the line to the street or septic tank. The sink is the easier path for the upstairs shower.