I have a problem, worse in the upstairs faucets than on the first floor. These are single lever faucets so there is a cartridge thatallows mixing cold and hot. I just replaced the two worse fauscets with new ones, but I still get hot when turning on cold. Cold one bad faucet cartridge among the remaining faucets be the problem. We built the house in 1977, and until recently it didn't do this. Any suggestions would be appreciated.