Cozy Low-Energy Shower

Step 14 C) Temperature Stabilization: Introduction

If you shut off the water at the showerhead, either with the foot pedal or with the more common "button" type valve on a low-flow showerhead, in some cases it will come back on much hotter or much colder than when you turned it off. If that happens, it could be because the hot and cold water supply don't have exactly the same pressure. If they are different, one can back feed into the other when water is turned off at the showerhead.

For example, in my system, the pressure in the hot water supply is higher. With the valve at the shower head turned off, the hot water feeds into the cold water pipe. When I turn the valve back on, I get scalded by 100% hot water, until the hot water has come back out of the cold water pipe. See the technical notes at the end (step 22) for more on why this happens, but more important is how to solve the problem: by adding a check valve (one-way valve) to prevent the back-flow. The following pages describe how to determine what you need and install it.

There are other possible solutions: a simple one is to only turn the flow way down, not completely off. For small pressure differences, that can work OK; but it still wastes some hot water, and the temperature stability may still be poor. Another option is to put in a thermostatic mixing valve to automatically maintain a constant temperature, but that's more expensive and more work to install. The check valve is a good compromise--reasonably easy to install, and works well to solve the problem.