Tankless Water Heater Maintenance Guide

Tankless water heaters were designed to be energy efficient. Compared with the traditional tank‐type heater — which cools down when not in use and must reheat the entire tank to maintain a hot temperature — a tankless unit provides hot water on demand and in a continuous flow until you turn off the faucet. But for all its advantages, it's key to note that energy efficiency doesn't equal maintenance‐free. In fact, the more attention you pay to preventive maintenance, the more certain you can be the tankless unit will remain efficient.

Below are some tips on proper care of your tankless water heater, along with some estimated times each task should take. The unit should be cared for on both the inside and outside, and most of these tasks can be handled on a yearly‐or‐as‐needed basis. Getting these tasks on your calendar periodically can help ensure a tankless water heater operating at optimal efficiency.


Exterior Maintenance

Wipe Cover (10 minutes)

Clean the outside of the unit with a cloth and nonabrasive cleaner periodically to prevent rusting. This is especially important in coastal areas where salt buildup can damage the metal. Touch up with paint as needed.

Inspect Pipes (10 minutes)

During cold weather, inspect the pipe insulation for any cracking and splitting. Although the insulation is designed to protect the pipes from freezing, it's a good idea to let a small amount of water run inside the house (also known as "dripping your faucet") when the weather is below freezing. Be sure the drip is running at the proper speed — fast enough to keep a continuous drip without making the hot water unit kick on.

Test Pressure Relief Valve (15 minutes)

The pressure relief valve needs to be opened and closed to ensure it is working. Operate the lever to allow the water to flow out onto the ground (be careful, because the water will be hot), then make sure the water shuts off when you close it.

Trim Around Unit (15–45 minutes)

If the unit is outside (as opposed to inside a garage or utility room), inspect the area around the unit and be sure there is at least 30 inches of clear space around it, trimming as needed. Some homeowners plant bushes or trees to hide the unit, but the clear space is needed for clean combustion air. Additionally, the plants often attract reptiles, such as lizards and geckos, which can get into the unit and cause it to malfunction. If your unit is indoors, you'll still need to check around the unit to ensure 30 inches of clear space and that no boxes/storage are blocking air flow.

Clean Air Filter (10 minutes)

Some units have a filter on the air intake that needs to be cleaned periodically depending on the surrounding area (pollen, dust, lint from laundry room, etc.). Simply wipe it clean with a damp cloth.

Descaling / Flushing Out Unit (1 hour)

Descaling or flushing‐out the water heater should be done at least once a year if you have hard water. Hard water refers to water containing calcium, magnesium, and other dissolved solids. In areas with soft water or if a water softener is installed in your house you might be able to go three or four years without needing to flush out your tankless water heater.

Did you know? Some tankless water heaters have scale detection software built in which will send you an error message letting you know it's time to flush (descale) your tankless water heater. Nifty!

There are many calcium, lime and rust removal products to choose from, never use any chemical that is not approved by the manufacturer of your water heater. Some manufacturers recommend white vinegar, still it is best to consult the user's guide to determine the manufacturer's recommendations.

Although isolation valves are not necessary for flushing out some tankless water heater heat exchangers, they make the job much simpler. If your tankless water heater does not have isolation valves already installed and the manufacturer of your water heater says you will need them then you will need to purchase and install them.

In order to flush out most tankless water heaters you will need a bucket, 2 hoses, and a small submersible pump to fit inside the bucket to circulate the descaling solution. We offer a fantastic all-in-one scale removal system that has the pump, hoses, and tank you'll need to get started.

For tankless water heaters WITHOUT isolation valves:

  1. Turn off the gas to the unit.
  2. If required, turn off the electricity to the unit. (Some manufacturers recommend turning the electricity off during the flush. Others recommend that it remain on. Consult the manufacturer's specifications.)
  3. Turn off the hot and cold water to the unit. Remove the hot and cold connections attached to the heater.
  4. Connect a hose from the pump outlet to the cold side.
  5. Connect a hose to the hot side and put the other end into the bucket.
  6. Put the pump into the bucket.
  7. Pour 3 to 4 gallons of white vinegar or the manufacturer recommended solution into the bucket. More, if needed, to make sure the submersible pump is completely covered with the descale solution.
  8. Plug the pump into an electrical outlet and allow it to push the descaling solution through the unit. Let the pump run and flush through the unit for between 45 minutes to one hour.
  9. Unplug the pump and remove it from the bucket.
  10. Disconnect the hose from the cold side.
  11. Pull out and clean the inlet filter.
  12. Put the filter back in.
  13. With the cold water still off reconnect the normal cold‐water supply connection.
  14. You now want to prepare to rinse out the descale solution from the unit.
  15. Keep the hose connected from the hot outlet into the bucket. Too make things easier, connect a longer hose to the hot outlet and put the other end into a sink or outside to drain.
  16. Slowly turn on the cold water and let it flush fresh cold water through the heater for a minimum of 5 minutes. If using the bucket, you will need to empty the bucket numerous times.
  17. Turn off the cold water and disconnect the hose from the hot side of the heater.
  18. Re‐attach the hot connection from the heater to the house.
  19. Turn on the gas. If the electricity was turned off, turn it back on at this point.

For tankless water heaters WITH isolation valves:

  1. Turn off the gas to the unit.
  2. If required, turn off the electricity to the unit. (Some manufacturers recommend turning the electricity off during the flush. Others recommend that it remain on. Consult the manufacturer's specifications.)
  3. Turn off both Isolation valves, remove the access port caps from both isolation valves.
  4. Connect a hose from the pump outlet to the cold side access port.
  5. Connect a hose to the hot side access port and put the other end into the bucket.
  6. Put the pump into the bucket.
  7. Pour 3 to 4 gallons of white vinegar or the manufacturer recommended solution into the bucket. More, if needed, to make sure the submersible pump is completely covered with the descale solution, open the access port valves.
  8. Plug the pump into an electrical outlet and allow it to push the descaling solution through the unit. Let the pump run and flush through the unit for between 45 minutes to one hour.
  9. Unplug the pump and remove it from the bucket.
  10. Close the cold side access port valve, disconnect the hose and replace the cap.
  11. You now want to prepare to rinse out the descale solution from the unit.
  12. Keep the hose connected from the hot water access port into the bucket. Too make things easier, connect a longer hose to the hot water access port and put the other end into a sink or outside to drain.
  13. Slowly turn on the cold‐water isolation valve and let it flush fresh cold water through the heater for a minimum of 5 minutes. If using the bucket, you will need to empty the bucket numerous times.
  14. Close the hot‐water access port valve, disconnect the hose and replace the protective cap. Then turn the hot‐water isolation valve on.
  15. Turn on the gas. If the electricity was turned off, turn it back on at this point.

Interior Maintenance

Clean Burner Assembly

Depending on the surrounding environment — areas with pollen or salt water, for instance — burner assembly cleaning may need to be done more frequently than once a year.

Please note: We do not offer instructions for cleaning your tankless water heater burner assembly. Our customers' wellbeing is of the utmost importance to us, and if this task is not performed by a licensed professional (i.e., a plumber with a gas license), your warranty may be voided or a dangerous gas leak could be created.


Related Items & Information

Frequently Asked Questions

Q. "I'd like to install a tankless water heater in my vacation home or cabin — is it possible to drain a tankless water heater to prevent freeze damage when not in use?"
A. Yes, on most brands (best to check first though with the manufacturer). Simply drain both lines to and from the unit. As long as there are no check valves in the way, that should drain the water from the unit. To guarantee that there is no water in the unit, we recommend two drain valves — one before and one after the unit — as well as blowing air through the water line.


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