Shower Temperature Fluctuations?

Question

The water temperature in the shower of my 14-year-old house changes to nearly pure cold whenever someone uses another faucet. The pressure is fine and when the other faucet is turned on there is no noticeable change in pressure in the shower. The main supply to the house is 1” and gradually reduces as the various cold water lines are split off. The water heater lines are ¾” and gradually reduce as the various hot water lines split off. All of the lines are copper.

I don’t remember this problem when the house was new, but my memory could be fading, or is it the water heater? I know there are temperature controlled shower valves, but would a pressure tank be a better solution. I would really like to take a comfortable shower while the rest of the house continues to function as well.

Answer 1

All your pipe sizing sounds correct and should be giving you enough volume. If you have enough hot water to shower normally and the only problem that is coming up is when another fixture is turned on, you get cold water to the shower, then I think the problem is the shower valve is not a pressure balanced valve. If the shower functions normally when no other faucets are opened, I'd be pretty certain of it.

A pressure balanced valve compensates for changes in water pressure, no matter how slight. At worst you will get a temp change of plus or minus 3 degrees. Putting a pressure tank on it may reverse the problem, all hot water. I would suggest replacing the valve with a pressure balanced type first.

Answer 2

Get youself a "posi temp" or similar self regulating controller, they're great. No freezing, no scalding. EVER.

While you're at it you may have to re-do your ceramics, depending on access to the plumbing pipes. If you run out of water, or have low flow, those are other issues, but bear in mind, depending on thr condiition of the water "hardness" or condition, a HWT replacement may be in the picture as well.