How to Flush and Clean a Water Heater

Turn Off the Power Source

The purpose of a water heat is to heat a large quantity of water using either gas or electricity as a fuel source. Before flushing the water heater, you need to turn off the fuel source to avoid damaging the water heater.

If you have a gas water heater, then look for a thermostat on the outside of the water heater. It typically has a red knob and is located where the gas pipe enters the unit. Make a note of what the temperature setting is, then turn the thermostat to the lowest setting, which should be marked as 'Pilot'.

If you have an electric water heater, then you will need to turn off the electricity from the breaker box or fuse box. Locate the branch breaker in the breaker box that is assigned to the water heater and turn it off. If you don't know which branch breaker is assigned to the water heater, then you will need to turn off the main switch to shut down power to the entire home.

For fuse boxes, you will need to remove the fuse that is assigned to the water heater. If you don't know which fuse is assigned to the water heater, you can turn off the power to the entire home by either turning off the main switch, or if there isn't a lever, removing the main fuse for the home. Just keep in mind that you will need to work with a flashlight or work lamp because the electricity will be off for the entire home.

Close the Water Supply Valve

With the heat turned off, the water heater can no longer heat the water inside the tank. If you are concerned about the risk of being burned, turn on a nearby faucet and allow the hot water in the tank to drain into the sink, while being replaced with cold water. This isn't a necessary step, but it is safer to work with cold water.

When most of the hot water has been replaced with cold water, turn off the water supply valve. This valve should be located where the cold water pipe enters at the top of the tank.

Attach a Garden Hose to the Drain Valve

Locate the drain valve at the base of the water heater and attach a garden hose to this valve with a set of channel locks. The drain valve generally looks like a regular hose bib, similar to an outdoor faucet, though it may be made of plastic instead of metal. If you can't spot it immediately, it may be hidden under a removable cover.

Connect the garden hose to the drain valve and extend the other end of the hose to an area where the tank can safely drain. Keep in mind that if you didn't allow the water to cool overnight or replace the hot water with cold water after turning off the power, then you will be dealing with scalding hot water.

Choose a place that will not be damaged by the force, temperature, or amount of water, and also cover the drain valve and hose connection with a towel to protect yourself from hot water and block any water that may spray from the connection.

Open a nearby hot water faucet to avoid creating a vacuum in the water lines that could keep water trapped in the tank. If you already opened a faucet to replace the hot water with cold water, then just leave the faucet open.

Open the Drain Valve to Drain the Water

The garden hose should be securely connected to the drain valve and the other end should be in an appropriate drainage location. Open the drain valve to begin draining the water out of the tank. The pressure-relief valve at the top of the water heater can be opened carefully to improve the flow of the water through the drain, but it's important to have a bucket under the discharge pipe to catch any water before it can drain onto the floor.

The drain valve may be several years old, so be careful to avoid straining the fixture. If it seems seized, don't just increase the force. You could break the valve, leading to a powerful spray and flood of scalding water.

A faulty drain valve is a job better left to a professional plumber or water heater technician, so if you run into this problem, you may need to put the job on hold until the valve can be replaced. For those DIYers that feel they could tackle the valve replacement on their own, just remember that if you rent your water heater, then the rental company may require you to call a licensed technician or plumber.

Test the Water

The goal of flushing the water heater is to clear out any sediment that has built up in the bottom of the tank, so after the water heater has been allowed to drain for about 10 to 20 minutes, fill a bucket up with water. Let the bucket sit for about 60 seconds completely undisturbed, then check to see if the water is clear and if there is any sediment in the bottom of the bucket.

If the water is cloudy or there is sediment in the bottom of the bucket, then you will need to keep draining the tank. Check again after another 10 minutes of draining. Repeat this process until the water is clear and there isn't any sediment in the bucket.

Close the Drain Valve and Remove the Garden Hose

Once the water is clear and there aren't any signs of sediment, you can close the drain valve and remove the garden hose. Make sure to keep the end of the hose directed up until it is outside or over a drain. Do not close the pressure-relief valve or the hot water valve in your nearby sink or bathtub. The valve and faucet will remain open to help bleed air from the line.

Open the Water Supply Valve

The hot water valve in your nearby sink or bathtub should still be open to help bleed air from the water line. Open the water supply valve and let the tank fill up. As it fills, the air in the top of the tank will be forced out gradually through the open faucet and through the pressure-relief valve.

Don't turn the power on until the tank is full. You will be able to tell when the tank is full because water will be flowing full pressure through the open faucet. At this point, it's safe to turn on the electricity to the water heater or turn the thermostat back to the original setting for a gas water heater.

Turn off the open faucet and close the pressure-relief valve, then wait about 20 to 30 minutes. Test water temperature at the nearest faucet.