Step-by-Step Water Heater Tank Flush
Annual maintenance you can do yourself to increase the efficiency and life expectancy of your water heater tank.
Procedure to flush the water heater tank
Turn “off” the water heater. GAS water heater: Turn the thermostat to the vacation setting, or to the lowest setting. Be sure to note where the thermostat was originally set. ELECTRIC water heater: VERY IMPORTANT - Throw the water heater breaker to OFF in the electrical panel. If this is not done, you will likely damage the upper heating element.
Shut-off the cold water supply to the tank. This valve is normally located directly above the water heater on the cold water inlet line.
Connect a garden hose to the water heater drain valve at the bottom of the water heater.
Place the other end of the hose in a floor drain, sump pit (with pump), or other receptacle that allows you to dispose of the water. Make sure no part of the hose or collection point is higher than half the height of the water heater tank. Otherwise, the water will not flow properly.
Go to the nearest hot water faucet and open it. Water should not flow out since you shut off the water (and thus the water pressure) to the tank in the first step. If water does flow out under pressure, then you didn’t shut off the correct valve. This open faucet will now serve as an air vent to allow the water from the tank to drain. NOTE: I do not recommend opening the water heater TPR valve (temperature pressure relief) on the top or side of the tank as a vent. These tend to leak or drip after being manually opened.
Open the drain valve to the water heater. Be VERY CAREFUL – the water temperature can cause scalding burns. The hose will become hot (use gloves). Make sure no one is splashed by the hot water coming from the hose. Water should flow out of the connected garden hose into your receiving point. If it does not, double check the previous steps.
Drain approximately half the water out of your tank. You can tell if half the water is drained by lifting the discharge end of the hose to half the height of the water heater. If the flow stops, then it is halfway drained. Do NOT completely empty the water heater because you will likely clog the water heater tank drain. Also, if it is a gas heater, the flame may come on and damage the tank if there is insufficient water in it.
Turn the water heater cold water inlet valve back on. This will begin to agitate the water in the tank and loosen the scale and buildup. More water will start to exit the drain hose – and you should begin to see sediment or discoloration in the discharge water.
Let the water drain from the hose until it starts to run clear – or a minimum of 5 minutes.
After the drain water runs clear, turn the water heater drain valve OFF. Your water heater will now start to refill with water. You will know your water heater is completely refilled when water starts running out of the hot water faucet you opened as an air vent
Turn the hot water faucet off after it has water running out of it.
Remove the drain hose.
Turn the water heater back “on”. Gas water heater: turn the thermostat back to where it was set. Electric water heater: throw the breaker in the panel back to the ON position
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