Getting the best out of any home appliance requires maintenance from time to time. That holds true for your hot water system. Whether you have a hot water tank or a tankless water heater, you’ll need to flush it annually to keep it running optimally. Need to know how to flush a hot water heater or how to flush a tankless water heater? We’ve got you covered.
Why Does My Water Heater Need to Be Flushed?
When a water heater is first installed, it’s clean, shiny, and new. Over time sediment builds up as a natural consequence of use. This sediment comes from the cold water that flows into the unit for heating. It’s not that the water is dirty, but all water contains trace amounts of dissolved minerals and minute particles. If you live in a hard water area, the mineral content is higher. As time passes, it builds up into sediment that collects at the bottom of the unit.
This sediment doesn’t necessarily affect the safety or quality of your hot water, but it can affect your hot water system’s efficiency. In particular, limescale causes damage to the heat exchanger in a tankless unit, making it less energy efficient and shortening its lifespan.
To keep your water heater running well, periodically remove any sediment that has collected at the bottom of your water heater or on the tankless heat exchanger by flushing it out and installing a descaler to reduce the amount of buildup in the system. This should be done once a year for most water heaters.
How to Flush a Water Heater Tank
To flush your water heater tank, you’ll need:
- A garden hose
- A bucket
- A kitchen colander
- A set of channel locks to fix the hose onto the tank drainage valve
Step 1: Turn off the Hot Water Tank
Before flushing the tank, first turn off the gas or electricity. This is important to prevent damage to the tank. This step is different depending on whether your tank runs on electricity or gas.
Electric water heater: If there’s a circuit switch for the tank, turn this off first. Then turn off the circuit breaker for the tank.
Gas water heater: Locate the thermostat, typically found at the bottom of the tank, and turn it off.
If you’ve turned your thermostat off, you’ll also need to find the gas valve that feeds gas to the heater and turn that off too.
Pro Tip: Dealing with the Hot Water
Since the tank is still filled with scalding hot water at this point, it can be unsafe to flush it right away. There are a couple ways to deal with this:
- Turn the tank off before you go to bed at night and flush it the next morning after the water has cooled.
- If prefer to do this task all in one day, open up one or more hot faucets and let the hot water run until it’s at a safer temperature before continuing.
Step 2: Turn Off the Cold Water Supply Valve
The next step is to find the cold water valve that supplies cold water to your tank and turn it off.
Step 3: Turn on a Hot Water Faucet
Locate the nearest hot water faucet that’s supplied by the tank. Turn it on, and leave it on for the duration of the flushing. This is important because otherwise a vacuum may form in the water line while the tank is draining. This can prevent the tank from draining and flushing properly.
Step 4: Attach Your Garden Hose to the Tank Drain Valve
The drain valve on a hot water tank is usually located at the base. Find this valve, and attach your garden hose using channel locks. Take the other end of the hose to whatever location you’ve picked out to drain the water. It could be a nearby tub or sink, a bucket, or a window leading outside.
Pro Tip: If you drain the hose into a tub or sink, use a kitchen colander to trap the sediment, rather than letting it go down the drain.
Step 5: Open the Drain Valve
WARNING: If you didn’t drain the hot water or wait for it to cool down, it will be scalding hot when you first start flushing the tank. This is extremely dangerous. If you’re working with hot water, make sure any exposed skin is protected.
Once your hose is securely attached to the drain valve and the other end is placed where you want it, you can open up the valve and start draining the water. Be gentle with the drainage valve. If it’s not opening easily, applying too much force could break it.
If drainage is very slow, you can try opening up the pressure relief valve a little. This should help the water come out at a faster rate.
Step 6: Check the Water for Sediment
Let the tank drain for about 10 to 20 minutes. Then fill a bucket up with draining water. Let the bucket sit for a couple minutes, then take a look. If the water looks cloudy or you see any sediment, keep draining the tank, then check the water again after another 10 minutes. Keep repeating this until the water is clear.
Once the water is clear and you don’t see any sediment, you can proceed to Step 7.
Step 7: Close the Drain Valve
Close up the drainage valve and remove the hose. Don’t adjust any other fixtures yet.
Step 8: Open the Water Supply
Open the water supply valve. This will start filling the water heater tank with cold water. As the tank fills up, air will be forced out the pressure relief valve and the open hot water faucet.
Keep going until the open hot water faucet is running cleanly with full water pressure. This ensures there’s no air left in the tank once it’s full.
Once the tank is full, turn off the faucet and readjust the pressure relief.
Step 9: Turn on the Tank
Finally, turn the tank back on. After around 30 minutes, opening up the closest hot water faucet should provide a small amount of hot water, verifying that the tank is on and heating.
When to Call a Professional Plumber to Flush a Water Heater Tank
Most of the steps involved in flushing a hot water tank are straightforward. Many homeowners can do this task themselves; it just requires the confidence to know you can.
If you’re not confident about flushing the tank, don’t worry! That’s why experts like the technicians at CW Service Pros are here! A professional plumbing technician can complete this job easily and get your hot water tank up and running afterwards.
It’s also best to call a plumber if you have any trouble opening the drain valve. Applying too much force to the valve can easily break it, which would require installation of a replacement part. It’s more cost-effective to have a professional help you get the valve open.
How to Flush a Tankless Water Heater
Flushing a tankless water heater is a different than flushing a water heater with a tank because you don’t have the benefit of the water in the tank to help drain sediment. Instead, you need to use a utility pump to flush the tankless unit.
The simplest way to flush a tankless water heater is to purchase a water heater descaler kit. These come with every component needed to flush the unit.
Alternatively, you can purchase the required items separately. You’ll need:
- A utility pump
- Channel locks
- A bucket that holds at least four gallons
- Several gallons of food-grade white vinegar
Before You Start
Check that your tankless water heater has the necessary isolation valves installed. These are valves that let you shut off the water or gas supply to the unit. They are important for completing the flushing procedure safely. If your tankless heater doesn’t have these, call a licensed plumber to get them installed.
Whether or not your tankless water heater has isolation valves depends on the model and the installation. If you’re not sure, it’s important to check before starting to flush the water heater. Isolation valves are clearly marked: The blue inlet valve is for cold water, and the red outlet valve is for hot water. Gas valves are usually yellow or red.
Step 1: Turn Off Isolation Valves/Gas/Electricity
Note: Isolation valves are open when the valve arm is parallel to the pipe. They’re closed when the valve arm is perpendicular to the pipe.
Gas: Turn off the electricity switch. Then close the gas, hot water, and cold-water isolation valves.
Electric: For an electric water heater, turn off the electricity switch, then close the hot and cold-water isolation valves.
Step 2: Connect the Hoses to the Water Valves
Connect one hose to the service ports on each of the cold water and hot water outlet valves. The service ports may be capped, in which case you’ll need to remove those caps before connecting the hoses.
Step 3: Connect the Cold Intake Hose to the Pump
Take the other end of the cold-water intake hose and connect it to the discharge port of the pump.
Drain the other end of the hot water outlet hose into a tub or sink, bucket, or outside.
Step 4: Add Descaler/Vinegar
If your descaler kit comes with a descaling liquid, add the recommended amount to the bucket.
Otherwise, add three to four gallons of plain white food-grade vinegar to the bucket.
Step 5: Flush the Water Heater
Open the cold and hot water valves, and then start the pump. You may need to adjust the bucket and hose as it starts up to make sure it’s all stable.
Allow the pump to circulate the descaler through the system. If you’re using a kit, follow the recommended guidelines for how long to let it circulate. It may be anywhere from 30 to 90 minutes.
If you’re using vinegar, keep the pump running for longer. Allow at least an hour to flush the system fully. If the pump runs at less than four gallons per minute, allow at least two hours.
Step 6: Flush the Cleaner
Once you’ve finished running the descaler through the system, turn off the pump.
Next, close both the hot and cold-water service ports. Then disconnect the cold-water intake hose from the intake valve.
Turn on the cold-water intake valve to let cold water start flowing through the system. This step is important because you need to flush out the remaining traces of vinegar or cleaner.
Let the cold water run for around 10 minutes. Once it’s finished, close the cold-water service port and the intake valve. Then remove the hose.
Step 7: Reconnect the Water Heater
To set up your tankless water heater and get it working again:
- Close and/or cap the hot- and cold-water service ports.
- Open the cold-water intake and hot-water outlet valves.
- Open the gas valve (if applicable).
- Turn on the electricity.
When to Call a Professional Plumber to Flush a Tankless Water Heater
Flushing a tankless water heater isn’t as straightforward a job as flushing a tank-style hot water tank. If you’re not confident with plumbing tasks or tools, it’s better to have a licensed plumber do the job instead.
In addition, you should call a plumber for advice if your system doesn’t have isolation valves for the cold-water inlet or hot-water outlet.
For Water Heater Advice or Expert Maintenance Services, Call CW Service Pros
Keep your home hot water system in good shape, and it will supply you with hot water for many years. When you need advice on your water heater system, or installation, maintenance, or repair services, call CW Service Pros. Our expert licensed plumbers have your back.