How Often Should You Flush a Water Heater in St. Charles?

Flush a tank water heater at least once a year. That is what A. O. Smith, a big water heater maker, says for most tanks. If your water is hard, flush it more often. City of St. Charles water tests at 152 mg/L of hardness, which counts as "hard." So in St. Charles, flushing every 6 months is a smart plan.

Hard water leaves minerals behind. They sink and pile up at the bottom of the tank as sediment. That pile makes the heater work harder, and it can make popping noises. If your tank is already loud, leaking or slow to heat, our water heater repair and replacement service can check it out.

At S&S Plumbing Systems in Saint Charles, we fix and replace water heaters across St. Charles County and St. Louis. Fall is a good time to flush, before the tank works hardest in winter.

How often should you flush a tank water heater?

Most tank water heaters should be flushed at least once a year. A. O. Smith's guide to draining a water heater says this, and it says hard water may mean you need to flush more often.

Your manual comes first. Different models can have different rules.

Is St. Charles water hard?

Yes. City of St. Charles water is hard. The city's 2025 Annual Water Quality Report, filed with the Missouri Department of Natural Resources, lists hardness at 152 mg/L. That sample was taken on September 12, 2023.

The U.S. Geological Survey sorts water hardness like this:

So 152 mg/L lands in "hard." That is about 8.9 grains per gallon, if you have seen hardness listed that way on a water softener.

This number is for City of St. Charles water. If you live in St. Peters, O'Fallon or another town, your water comes from a different supplier. Look up your supplier's yearly water quality report to see your own number.

What happens if you never flush a water heater?

If you never flush a water heater, sediment keeps piling up in the bottom of the tank. A. O. Smith lists these signs of buildup:

• Popping, rumbling or banging sounds from the tank
• Water that looks rusty or dirty
• Hot water that takes longer than normal to heat up

A thick layer of sediment sits between the burner or element and the water. The heater has to run longer to heat the same water. If you hear popping, it is a good time to flush it or have it checked.

How do you flush a tank water heater?

You can flush a tank water heater in a few steps. A. O. Smith's draining guide covers the key ones: shut off the heat, hook a hose to the drain valve, and open it. Check your manual first, since your model may differ.

1. Turn off the heat. On an electric heater, flip its breaker off. On a gas heater, turn the thermostat dial to "OFF."
2. Let the water cool. The water in the tank is hot enough to burn you. Give it time.
3. Turn off the cold water going into the tank. The shutoff valve is on the pipe at the top.
4. Hook a garden hose to the drain valve. The drain valve is near the bottom of the tank. Run the other end to a floor drain or outside.
5. Open a hot water faucet in the house. This lets air in so the tank drains faster.
6. Open the drain valve. Let the water run out until it looks clear.
7. Close the valve, refill, and turn the heat back on. Turn the cold water back on and let the tank fill all the way before you turn the power or gas back on.

If the drain valve will not open, drips after you close it, or the water never runs clear, stop there and call a plumber.

Do tankless water heaters need to be flushed too?

Yes, but in a different way. A tankless water heater does not hold a tank of water, so there is no sediment pile to drain. Hard water can still leave scale inside it. Most tankless makers call for a cleaning that runs a solution through the unit. Your manual will say how and when. Learn more about our tankless water heater installation work.

FAQ

How often should I flush my water heater if I have a water softener? Softened water has fewer hard minerals in it, so sediment builds up slower. Plan on at least once a year, and follow your water heater manual.

Is it too late to flush an old water heater that has never been flushed? Not always, but an old tank that has never been flushed can have a lot of sediment. The drain valve can clog or start to leak once it is opened. It is a good idea to have a plumber look at it first.

Can flushing a water heater stop the popping noise? Often, yes. A. O. Smith lists popping and rumbling as signs of sediment, and flushing removes sediment.

How do I know how hard my water is? Look up your water supplier's yearly water quality report. In Missouri, many are posted on the Missouri DNR site. City of St. Charles water lists 152 mg/L.

Do I need a plumber to flush a water heater? Many people do it themselves. Call a plumber if the drain valve sticks, leaks or clogs, or if you are not sure how to shut off the gas or power.

Need help with your water heater?

If your water heater is popping, leaking or running out of hot water, call S&S Plumbing Systems at (636) 246-1439. We can check the tank and tell you if it needs a repair or a replacement. Learn more about our water heater repair and replacement work, or request service online.