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Stacking or short-cycling

Applies to tank-type gas and electric water heaters
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Gas water heater ECO

Electric water heater ECO
There is a water heater condition called stacking.

Stacking is caused with repeated short draws of hot water.
Each time hot water is drawn out of faucet, cold water immediately enters bottom of water heater tank through the dip tube.
Dip tube is a plastic pipe connected to cold water inlet. Cold water enters at bottom of tank.
So cold water enters bottom of tank near gas water heater thermostat, or near lower thermostat on electric heater

How stacking occurs:
Let's say water heater if fully heated and burner or elements are turned off.
A short draw of hot water causes cold water to enter tank.
Another short draw. And then another short draw, each draw happens near same time as other draws.
Water at top of tank is plenty hot, but bursts of cold water cause thermostat to turn on burner or element.
Water heater heats more hot water, and more hot water rises to top of tank.
Top of tank was hot before, but with added heating, the water becomes hotter than usual.

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Water at top of tank becomes overheated each time stacking occurs.
This can cause TP valve to release water, and cause ECO energy cut-off to trip on upper thermostat of electric water heater.

Stacking may not be the cause of your water heater problem.
However, remember if single-handled faucet is opened straight upward, then that will draw both hot and cold water out of water lines.
As soon as hot water runs out of faucet, cold water enters tank. This is ingredient for stacking, and is energy-wasteful.

Crossover can cause stacking.
Only when single-handled faucet is lifted with handle fully to the right, does faucet draw only cold water.
But some single-handled faucets have 'crossover' between hot and cold sides because of defect faucet cartridge.
When crossover is present, hot water draws each time any faucet in house is turned on.
To test for crossover: Turn OFF water to heater. Cold water pressure is still ON.  Next, turn on hot side of all faucets in house and wait 10 minutes and check for water flows. There should be no water flowing. If water flows, then that means one or more faucets has crossove problem. To test which faucet, turn off all faucets except hot side on one faucet. Put ear against each single-handled faucet in house and listen for flowing water. Also check mixing valve on water heater if one is installed. Defective check-valve can also cause crossover.
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