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How to Drain a Water Heater

In this how-to video, This Old House plumbing and heating contractor Richard Trethewey shows a quick and effective way to drain a sediment-filled electric water heater.

Should you drain your water heater? Yes. You should do it once a year, sometimes more if you have hard water, to prevent scaling and sediment from accumulating inside the tank.

Sediment sometimes looks like sand, but it is made up of minerals from your home’s water supply. These minerals don’t dissolve, and subsequently, turn into particles inside your unit.

Unfortunately, this build-up can cause significant problems if left unchecked—costing you time and money by shortening the unit’s efficiency and functionality, and potentially causing the water heater to fail prematurely.

In this video, This Old House plumbing and heating contractor Richard Trethewey explains how to drain and flush a water heater.

How to Flush a Water Heater:

  1. Before you tackle any service to the water heater, turn off all of the electricity to the unit, including the breaker. Turn off the cold water supply and allow the heater to cool (this may take a couple of hours).
  2. Locate the water heater’s drain valve, typically found near the bottom of the tank. If you don’t have a floor drain, thread a standard garden hose to the valve to drain the water from the tank and direct it into a bucket. Many can simply use gravity to drain water from the unit into a bucket but if you want to pump the water outside (making the discarding of the unwanted water easier), follow the connection instructions from the pump manufacturer. Open one or two hot water faucets in the house to prevent damage to your pipes.
  3. Open the drain valve and inspect the water for sediment. If the water is full of sediment or is not clear, refill the heater and drain it again. To stir up sediment that has settled on the bottom of the tank, turn the water shut off valve on and off a couple of times.
  4. Continue to fill and drain the heater as often as necessary until the water runs clear. If the unit is in good shape, one flushing is generally enough and you won’t have to flush it again for one year. If you see an excessive amount of sediment though, you may want to consider adding a water filter or a treatment system to your home or it may be time to call in a professional for advice.
  5. Once the water runs clear and the unit is empty, disconnect the hose and the pump. Close the drain valve, and refill the tank before turning on its power source.
  6. Turn on the electricity to the water heater. Performance should resume as usual, except for some initial air pockets that will be released through the faucets. Generally, that air will be purged within a few seconds, and then full water flow will resume. Turn off the water taps you had previously opened.

How to Tell if Your Water Heater Has Sediment Build-Up

There are a variety of indicators that your water heater has a sediment build-up including:

  • Energy bills go up despite no increased usage
  • Hot water runs out prematurely
  • The water heater makes noise while it’s running
  • Your hot water looks rusty or has a bad odor
  • It takes a long time for the hot water to warm up
  • The water temperature is inconsistent and fluctuates

Draining a water heater is a relatively easy task that homeowners can tackle, but if the water doesn’t drain or the heater’s performance issues don’t improve after flushing the unit, a professional will be able to identify other potential problems that may not be recognizable to the homeowner.