All the water lines were fine when we started to remodel this house. Everything worked.
All pipes are copper.
1 . We disconnected a hot and cold water line that went from the basement to the first floor that was used for a washing machine. We cut them off in the basement and capped them. There was a washer/dryer hookup in the basement so we wanted to use them instead.
2. We disconnected a hot water tank in the basement and capped the line. The hot water is now running off the furnace.
The shower and tub were working fine.
NOW, after removing what we did, when we use the shower/tub (which has a one handle American standard mixing value) makes all the pipes BANG / RATTLE AND VIBRATE. IT IS EXTREME AND YOU CAN SEE ALL THE PIPES IN THE BASEMENT MOVING.
It ONLY happens when we MIX the hot and cold.
It should also be noted that if we use just the cold or just the hot, it does not happen.
We have tried replacing the cartridge and that did not work.
There is also REDUCED FLOW in the COLD WATER LINE ONLY in the shower/tub.