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How to Maintain a Tankless Water Heater? – 5 Steps

Fact checked by Stephen Conklin

how to maintain a tankless water heater

How to maintain a tankless water heater is a competency that not many new owners get the hang of. Some think a tankless water heater doesn’t require maintenance because it has no storage tank where sediments and limescale could accumulate.

With or without mineral buildup, maintaining a tankless water heater is essential as part of a comprehensive preventive maintenance system. After all, this unit still has pipes where sediments can accumulate.

So how do you maintain, clean, and descale tankless water heater units? We have five steps to help you. Please continue reading.

Table of Contents

Step-by-step to Maintain a Tankless Water Heater

What to prepare


Annual maintenance of a tankless water heater doesn’t require much. Prepare the following items:

  • 2 hoses
  • a bucket
  • a recirculation pump
  • a flush solution (i.e., undiluted white vinegar) to keep the interior pipes in good condition.
  • your tankless water heater’s manual (it contains a maintenance checklist to keep the appliance in optimum condition)

Or, you could buy a kit specific to your unit.

Let’s get right to the steps.

Step 1. Prepare the tankless water heater.


1. Close the natural gas supply valve or the propane control knob if you have a gas tankless water heater.

For electric units, cut off the electricity by flipping the corresponding circuit breaker switch to OFF.

2. You can look at the appliance for three pipes running from the bottom. Or, read the User Guide/Manual to determine the location of the unit’s water valves.

3. Look for three colored straight handles or knobs: red for hot, blue for cold, and another color for water distribution.

4. Twist all three valve handles so they run parallel to the pipe. This action stops the water from entering the heater.

Step 2. Remove the tankless water heater purge port valve covering.


Tankless units don’t have a drain valve at the bottom for draining, flushing, and cleaning a tankless water heater. Instead, these appliances have a “purge port.”

1. Read the User Guide for the precise location of the purge ports. Most units have these components on the water valve assembly we mentioned in Step 1.

2. Look for a small colored T-shaped handle. Then twist it until it runs parallel to the purge port.

Please do not skip this step, as it’ll ensure your protection from scalding water.

3. Hold the purge port covering and gently pull it to remove it. Please don’t use excessive force, as you might dislodge the port’s rubber washer.

4. Remove the caps of the two other purge ports.

Step 3. Prepare the flushing setup.


Most tankless water manufacturers include purging lines with their products as part of a maintenance kit. If yours didn’t, you might want to check the purge port’s diameter and buy the correct size hose. You’ll need two hoses.

  1. Read the manual for specific instructions on connecting the hosing lines.
  2. Ensure the flexible pipe is long enough to reach the bucket.
  3. Connect one hose to the blue purge port and its other end to a recirculation pump.
  4. Pour undiluted white vinegar into a bucket. Two and a half gallons should be enough to circulate through the tankless water heater’s interior pipes.
  5. Secure another hose to the red purge port and place its other end in the undiluted vinegar-filled bucket.
  6. Submerge the recirculation pump into the vinegar.

Pro Tip: Although some resources recommend using a commercially available tankless water heater cleaner, we don’t advise it to remove mineral buildup and sanitize the appliance, considering that its residue can get into your drinking water. Distilled white vinegar is safer and equally effective.

Step 4. Flush the tankless water heater.


You’re now ready to tune up (descale, flush, and clean) the tankless water heater.

1. Twist the red and blue water port valves to run perpendicular to the pipe. This action helps recirculate the vinegar solution through the tankless water heater’s internal pipes.

2. Check the manufacturer’s guidelines on reestablishing electrical power to the heater. Some brands need electricity to open electronically-controlled valves inside the appliance.

3. Turn on the recirculating pump. The powerful motor draws the distilled white vinegar from the container and pushes it through the tankless water heater’s heat exchanger.

After circulating through the pipes, the vinegar will exit through the hot purge port and back to the bucket.

4. Wait 45 minutes to an hour.

Step 5. Finish up.


Forty-five minutes might seem long, but it ticks off one of the boxes in your tankless water heater maintenance schedule. Completing this task involves doing Steps 1 to 4 in reverse.

  1. Repeat Step 4 one last time, using clean water instead of distilled vinegar. This action will help remove the vinegar’s residue in the pipes.
  2. Switch off the recirculating pump.
  3. Twist the purge port valve handle parallel to the pipe to close the water.
  4. Remove the hoses from the tankless water heater purge ports.
  5. Empty the bucket down a floor drain.
  6. Reposition the purge port cap and secure them properly.
  7. Twist the hot, cold, and water distribution valve perpendicular to the water pipe to allow water to enter the tankless water heater.
  8. Reestablish fuel supply or electricity to the tankless water heater.

We found this YouTube video by Any Hour Services that can help you maintain and flush a tankless water heater like the pros.

Frequently Asked Questions


How often should I service or maintain my tankless water heater?

How often you must service your tankless water heater depends on several factors.

Although most experts recommend a yearly maintenance regimen, some brands might suggest more frequent servicing to address and prevent mineral buildup.

On that note, it’s ideal to flush a tankless water heater twice a year if it has a high concentration of minerals and sediments.

How much will I spend maintaining my tankless water heater vs. hiring a professional?

Professional service for tankless water heater can cost about $150 to $250.

The advantage of such an approach is convenience. Plumbers work while you resume daily activities. Moreover, $250 annually doesn’t sound “pricey.”

DIY tankless water heater maintenance doesn’t entail a huge expense.

You can buy a gallon of distilled white vinegar for less than $4, making 2.5 gallons $10. A small recirculating pump can set you back by about $200. However, you can always borrow from a neighbor or friend.

Maintaining a tankless water heater yourself is more practical unless the manufacturer requires professional servicing to retain warranty coverage.


You’ll never second-guess how to maintain a tankless water heater again. The steps outlined above should make you confident enough to service a tankless water heater without calling a professional. Of course, you’re welcome to hire one.

Although tankless water heaters last longer than storage tank types, these appliances still require periodic maintenance.

Flushing these appliances at least once yearly should help you get the most out of them, enjoying on-demand hot water for everyone in the household.

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