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Water heater temperature controller

Sep 1, 2009

We have lived aboard our Corbin 39 cutter Cormorant since 1997, and for several years endured showering

aboard with wildly fluctuating water temperatures. At first it was icy cold, then scalding hot from the engine-heated water heater, and no amount of adjusting the hot and cold taps would produce a comfortable temperature. I finally purchased a tempering valve (also known as an attemperator), which is a beautifully-made brass device which blends cold water with the hot water from the water heater to obtain and hold a constant temperature. It even has an adjustment dial on it to select warmer or cooler water. It's a thermostatically controlled safety valve that prevents crewmembers from being scalded by the 180° F water in the engine-heated water heater. 

On my first attempt at installing the tempering valve, I located it on a convenient bulkhead in the engine room, a few feet from the water heater. Unfortunately, I could not get the valve to properly regulate water temperature. Reluctantly, I removed the tempering valve and stored it away.

Last year I happened to see an advertisement for a marine water heater that had an optional tempering valve located on the water heater itself. Believing that this manufacturer surely knew more about his business than I did, I re-installed the tempering valve as close to the hot water outlet on the water heater as possible. Viola, the valve works perfectly! Turn on the shower hot water tap only, and leave the cold water tap on the shower control closed. 

Note that the tempering valve can only function when water is flowing through it, so you will have to allow the cold water in the supply piping to pass through until the warm water reaches the shower head. We collect the cold water in a container and use it elsewhere. Water is much too valuable to waste on a voyaging sailboat!

While the installation is far from beautiful, it is leak-free thanks to the liberal use of Loctite 567 (also sold as Loctite PST) and Teflon (PTFE) tape on the pipe threads. Do not try to solder the pipe connections as heat will damage the internal parts of the tempering valve. To obtain "guaranteed leak-free threaded connections" try the following method.

Clean the male threads with a wire brush and acetone or similar solvent to ensure a clean starting surface. Apply a thin coat of Loctite 567 to the male threads only, followed by three layers of Teflon tape, and finish with a second thin coat of 567 over the layers of tape. Make up the connection and let it sit for 24 hours before applying pressure water. This method works even with threads in poor condition, and believe me when I tell you that all you will find outside the USA are poorly cut threads. Do not use Loctite 567 on plastic threads as it will attack some plastics. By the way, this method works equally well on gasoline, diesel and LPG piping. 

Water tempering valves and pipe fittings can be purchased from plumbing supply stores, and Loctite 567 and Teflon tape are available at any auto parts store. Be sure to specify a tempering valve for use with unequal cold to hot water pressures.


About the author:

Harry Hungate and his wife Jane Lothrop are now enjoying comfortable showers aboard their Corbin 39 Cormorant. They departed Thailand in early January 2009, crossed the Indian Ocean and Red Sea, and plan to spend the next couple of years in the eastern Mediterranean.

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