Q: When anybody is taking a shower and someone turns on the faucet or flushes the toilet, the water in the shower turns hot and scalds the person showering. My home was built in 1986 and I was wondering if there was something my contractor didn’t do to the plumbing that would cause this to happen. I am planning to remodel my bathrooms in the next couple of months and would like to know if there is something that can be done to resolve this problem.
A: Generally, homes with low water pressure may experience the problems you outlined. Many residential plumbing systems are configured with a main pipe that has a larger diameter than the branch pipes that go to each fixture such as the toilet, sink or shower. The larger pipe carries a larger volume of water when multiple fixtures are on at the same time, thus reducing the effect of scalding and low water pressure.
This remains true for all modern water supply pipe materials such as copper, PVC (polyvinyl chloride), CPVC (chlorinated polyvinyl chloride) and PEX (a form of cross-linked polyethylene) pipes. Water volume in older homes is often reduced if the home has galvanized water pipes. Corrosion and calcium buildup inside galvanized pipes reduce the area inside the pipe, reducing the amount of water available to the fixtures. This can be remedied by replacing older galvanized pipes. Start with the horizontal pipes, as they are more likely to become restricted.
A licensed plumber can answer your questions by simply doing a visual inspection of the plumbing. Until the bathroom has been remodeled, you can reduce the chances of scalding by limiting the water flow to the toilet by partially closing its supply valve (generally located on the wall or floor behind the toilet tank). This will cause the toilet to refill slowly. More importantly, add an “anti-scald” showerhead or tub faucet to protect against accidental scalding. Modern faucets typically have this feature built in, but it can also be added to existing faucets.