Why and How Often to Flush a Water Heater

Key takeaways

Hard water leaves mineral sediment that makes the tank noisy, slower, and more prone to corrosion.
Once a year is a common baseline, and harder water may call for more often.
Turn off the gas or the breaker first, and remember the water in the tank is hot.
If the drain valve is stuck, leaks, or has never been used, have a plumber handle it.

What sediment does inside the tank

Much of Ohio has hard water, and the hardness varies by town, so your utility's water quality report is a good place to check. Hard water carries dissolved calcium and magnesium. When water is heated, some of those minerals drop out and settle as sediment on the bottom of the tank.

In a gas heater, that layer sits between the burner and the water, so the burner runs longer to heat the same amount. In an electric heater, scale coats the lower element and can shorten its life. Either way, the layer can trap water that boils beneath it, which causes rumbling and popping. It also holds moisture against the steel, which speeds up corrosion. The result is less hot water, higher energy use, and a shorter lifespan. If you hear those noises, signs your water heater is wearing out explains what else to look for.

How often to flush

Once a year is a common baseline for a tank heater. If your water is hard, flushing about every six months may keep sediment from building up. If you have a water softener or other treatment, the tank collects less scale and once a year is usually enough. Softened water can use up the anode rod faster, so check the rod when you flush.

The best habit is to flush on a schedule, such as at the same time you change smoke detector batteries. If the heater is many years old and has never been flushed, do not assume it is as simple as it sounds. Old sediment can be packed hard, and a drain valve that has never been opened may leak when it is. That is a case for a plumber.

How to flush a tank heater

Water from the bottom of the tank can be hot enough to scald, so let it cool for a couple of hours first or drain slowly into a safe place. The general steps are:

Turn off the power. For electric, switch off the breaker. For gas, set the control to pilot or off. Never leave an electric heater powered with the tank partly drained, because the elements can burn out.
Close the cold water supply valve at the top of the tank.
Attach a garden hose to the drain valve near the bottom and run it to a floor drain, a laundry sink, or outside. Check that the hose can handle hot water and runs downhill.
Open a hot water faucet somewhere in the house. This lets air in so the tank can drain.
Open the drain valve. Water may come out cloudy or with grit. If it slows or stops, close the valve and call a plumber, since the drain may be clogged with sediment.
Let it run until the water comes out clear. Briefly opening the cold supply valve to stir up sediment is a common step, but go slowly.
Close the drain valve, remove the hose, and reopen the cold supply. Leave the hot faucet open until water flows steadily, which clears the air out of the tank.
Restore power or relight the pilot, following the instructions on the heater label.

When to call a plumber instead

Leave the flush to a plumber if:

The drain valve is stuck, plastic and brittle, or drips after you close it.
The heater is old and has never been flushed.
You smell gas, or you are not sure how to shut off or relight the unit safely.
Water stays cloudy after draining a long while, or the tank will not drain at all.
The heater is in a spot with no safe place to drain, such as a basement with no floor drain.

A plumber can also swap a failing drain valve for a full-flow valve that drains sediment more easily, check the anode rod, and test the relief valve. If scale is a recurring issue, water treatment reduces what reaches the tank, and water heater service covers repairs and replacement.

Other checks while you are there

A flush is a good time to look over the rest of the unit. Check the anode rod if you can reach it, since a mostly bare rod means the tank is no longer protected. Look at the connections and the base for moisture or rust. Lift the lever on the relief valve briefly with its discharge pipe in place, and a little water should flow and stop. If it keeps dripping afterward or does not move at all, have a plumber replace it. Do not cap the discharge pipe. Finally, check the temperature setting. Many households use about 120 degrees Fahrenheit.

Frequently asked questions

Will flushing fix a noisy water heater?

It often helps when the noise comes from loose sediment. If the sediment has hardened or the tank is old, the noise can return. A plumber can tell whether the tank is worth saving.

Do I need to flush a tankless water heater the same way?

No. A tankless unit has no tank to drain. It is descaled by circulating a cleaning solution through its heat exchanger using service valves. Follow the manufacturer's schedule or have a plumber do it.

Is it safe to flush a water heater myself?

It can be, if you turn off the power or gas, let the water cool, and drain to a safe place. Hot water can burn, and old drain valves can fail. If anything seems stuck or unsafe, stop and call a plumber.

4 min read.