Water temperature, old pipes

QUESTION: The water in our showers ranges from extreme cold to extreme hot without us turning the knob. This happens in both bathrooms. The water heater is about 12 years old. What causes this and how can it be fixed?
Liz Irons, Elk Grove
ANSWER: “I doubt that your water heater has anything to do with the shower problem,” says Vince McDonald of McDonald Plumbing, Heating and Air Conditioning in Sacramento. “My guess is that you also have low water pressure and possibly an older plumbing system, or perhaps one which is not properly engineered to deliver water to your showers without large temperature fluctuations. One option is to install pressure-balanced shower valves. These valves have been required on all new construction and remodels for the past couple of years. They automatically adjust the hot-water flow through the valve when the pressure fluctuates.”
“I suspect that the root of the problem is more serious. Older homes often have a galvanized steel piping system that gets clogged with corrosion, causing lower water pressure and greatly reduced flow. When you hop in the shower, the system, with its capacity to deliver adequate water flow, is overwhelmed when another plumbing fixture in the home is used at the same time,” he says. “There is only so much water that this troubled system can deliver, and it currently is just not enough,” he says. “Make sure that you announce to everyone in your home that you are going in the shower and ‘Don’t run anything!’”
“The best way to resolve this problem is to have your plumber change the water piping system. It needs to be designed according to current sizing methods and tables found in the Uniform Plumbing Code. Simply replacing the old pipes with new pipes the same size may not be enough. If your home does not have galvanized pipes, then it is possible that it was not properly engineered and sized. Consult with a licensed, reputable plumbing firm. They should be able to properly diagnose your problem and provide you with options and a written estimate.”

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