How to Flush a Water Heater

Your tank-style water heater spends its life doing its job in solitude, but even though it doesn't demand much attention, you shouldn't ignore it completely. Its very passivity makes it vulnerable to internal deterioration from rust and scale.

Water heater in the basement.
credit: R Willis
Regularly flushing your water heater adds years to its service life.

Hard water deposits collect in virtually every water heater, producing sediment that tends to collect on the bottom, affecting the performance of the heater and the quality of the water. Rust also settles, eventually turning the hot water an unappetizing yellowish or brownish color. You can't completely prevent rust or scale from forming, so you have to protect the tank by flushing it periodically. That keeps your water heater performing optimally, and it will prevent, among other things, brown-water stains on the clothes you wash.

Know When to Flush

Calcified bathroom fittings in a hotel
credit: andhal/iStock/GettyImages
If your faucets are calcified, the same is probably true of your water heater.

To keep your water heater in tip-top shape, you should flush it at least once a year—more often if you have a large household with high water demand. Few homeowners actually do that, and they eventually experience the following symptoms of excessive sediment accumulation:

  • Brown/yellow hot water: The brown coloration is caused by iron. It's common in well water, and can often be controlled by a water softening system. If it's only in the hot water, it might be coming from the pipes or the water heater. Suspect the water heater if the hot water at every faucet is uniformly discolored.
  • Low flow: Scale collects inside the outlet ports on the tank and restricts water flow. In homes with galvanized plumbing, pipe corrosion can be partially responsible, but if you notice low flow only in the hot water, it's probably the water heater.
  • High energy bills: Sediment on the bottom of the tank interferes with heating, especially if you have a gas water heater. The burners stay on longer, and you pay more for gas or electricity.

How to Flush

Draining a water heater.
credit: Andrew Penney Photography
Direct the tank water to a safe drainage point using a garden hose.

Flushing a water heater is a task that any homeowner can perform. The basic procedure calls for little more in the way of tools than a garden hose and some pliers to turn a stuck drain plug.

Step 1 Let the Water Cool

Turn off the water heater. If you have an electric one, just turn off the breaker in the panel that controls it. For gas models, turn the dial on the water heater to the off position and turn off the gas valve. Let the water cool for about 24 hours.

Step 2 Attach a Garden Hose

Screw the hose to the drain plug on the bottom of the tank and extend the hose to a place from where the water can drain, such as a floor drain, a utility sink or somewhere outdoors.

Step 3 Shut Off the Water and Open the Drain Plug

Turn off the cold water valve to the water heater and open a hot water faucet somewhere in the house to allow air into the pipes. Open the drain plug and let water drain out. It could take 30 minutes to one hour for all the water to drain.

Step 4 Flush with Cold Water

Close the hot water faucet and open the cold water inlet. Let cold water flow through the tank and out through the hose until it runs clear.

Step 5 Refill the Tank and Turn the Power Back On

Remove the hose and close the drain valve. Turn on the cold water and let the tank fill. When you have full pressure at the hot water faucets, turn the breaker back on or, if you have a gas water heater, open the gas valve and relight the pilot.

Getting Rid of Sediment

Shop vacuum.
credit: mc0081
Suck out sediment with a wet/dry vacuum.

If a large amount of sediment has accumulated on the bottom of the tank, you may need to improvise a suction device to extract it. You can make one using a shop vacuum, a 2-foot length of 1/2-inch polybutylene tubing and some duct tape. Use the tape to make an airtight connection between the tubing and the end of the vacuum hose.

To extract the sediment, unscrew and remove the drain plug, insert the 1/2-inch tubing through the hole and turn on the vacuum. Move the tubing around inside the tank to suck up as much of the sediment as you can. When you're done, wrap plumbing tape around the plug and tighten it back in place with a wrench.

Do a vinegar flush: If you haven't serviced your water heater for many years, it's a good idea to flush it with vinegar. To do this, unscrew and remove the temperature and pressure-relief valve when the tank is empty and pour in two gallons of distilled white vinegar. If your tank has a side-mounted T & P (temperature and pressure) valve, it may be easier to remove the anode rod and pour the vinegar through that port instead. Replace the T & P valve or anode rod, fill the tank with cold water and let the vinegar/water mixture sit for a day before draining the tank and refilling it with clean water. The vinegar solution will dissolve all the hard water deposits and rust that may have collected on the sides of the tank liner.


Chris Deziel

Chris Deziel

Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.