How to Maintain a Tankless Water Heater

Last Updated: December 20, 2022

Over time, a tankless water heater can accumulate minerals that can build up on and erode the walls inside your tank's heating chamber. To properly maintain and clean your tankless water heater, you must flush and remove the mineral deposits from your tank at least once per year. Continue reading to learn how you can maintain your tankless water heater to ensure its optimal performance and efficiency.

Steps

1
Turn off the power source for your tankless water heater.^{[1]
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- This can be done by shutting off the main gas or turning off the circuit breaker for electrical devices.
2
Close and turn off the 3 water valves attached to your tankless water heater.^{[2]
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- This procedure will prevent cold water from flowing into the water heater and prevent hot water from coming out during the cleaning process.
- The water valves consist of a cold water valve that may be colored blue, a hot water valve that may be colored red, and a third main valve that runs the water into your home.
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3
Remove the purge port valve caps slowly from the purge valves located on each of the cold and hot water valves.
- The purge valves have small handles that resemble the letter "T."
- This procedure is done to relieve any pressure that has built inside the valves and will prevent excess hot water from shooting out and coming into contact with your skin.
- There may be pressure when removing the purge port valve caps, so it is extremely important to make sure the hot water valve is completely and accurately shut off for safety purposes.
- Handle each cap carefully to make sure the rubber washer sealing discs stay in place, which are needed for your valves to function properly.
4
Attach your hosing lines to each of the 3 valves.^{[3]
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- If the manufacturer of your tankless water heater did not provide you with hosing lines, you can purchase them from any retail store specializing in home repair or water heaters. The hosing lines must be long enough to reach between the water heater and your bucket.
- You may need to consult your manual provided by the tankless water heater's manufacturer or contact the manufacturer directly for exact instructions regarding this procedure.
- In some cases, this procedure may require you to use a sump pump and connect hoses that will discharge and flush water from the tankless water heater using the cold and hot water valves.
5
Open the purge port valves by twisting them perpendicularly to the position of the cold and hot valves.
6
Use 2.5 gallons (9.46 liters) of undiluted white vinegar to clean your tankless water heater at all times instead of chemical solutions.^{[4]
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- Since your tankless water heater is most likely the source of all your drinking water and bathing water, using chemical cleaning solutions may be extremely harmful to your health.
7
Perform the flushing and draining procedure by following the directions provided by the manufacturer of your tankless water heater.
- This procedure may take up to 45 minutes.
8
Close the purge port valves by twisting the "T"-shaped handles after the flushing process has been completed.^{[5]
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9
Disconnect and remove the hosing lines from each water valve.
10
Replace the purge port valve caps onto the purge valves.
- Tighten the caps completely and firmly without breaking the rubber sealing discs located inside the caps.
11
Refer to the manufacturer's manual of your tankless water heater for exact instructions on how to safely re-start your water heater.
- This procedure may just require you to rotate and open the cold and hot water valves so they are parallel to the position of the main valve that leads into the house.
12
Turn on the hot water tap in your sink slowly to allow the air to pass through the pipe.
- Continue to run the water until it runs steadily without air escaping.
- This procedure may take up to 2 or 3 minutes.

Community Q&A

Question

What do I do if there is water leaking and steam comes out when the hot water is in use?

Community Answer

Your heat exchanger has cracked and needs to be replaced. You can buy just that part, or replace the whole tankless heater. Replacing just the part is less expensive (for parts), but I replaced the whole unit because the water had leaked onto the electronics, and who knows when that would cause another failure.
Question

Do I need to do this even if I have a water softener?

Community Answer

Yes, as it's important to properly maintain a tankless water heater. The heating elements get extremely hot and bake calcium and other deposits on the heating units quickly. Filtering even clean municipal water should be done. Neglecting to maintain a tankless heater results in a very short life span. They're a very sensitive piece of machinery and require you to maintain them. Install a filter before the heater and clean them twice a year for a long lifespan. It is required. You're cleaning baked on junk off the heating element more so than dirt or debris.
Question

After flushing a Rinnai tankless water heater with white vinegar, can I store and reuse the vinegar next time?

Community Answer

No, the used vinegar has dissolved solids in it and is no longer "virgin." Discard the used vinegar and always use fresh vinegar for flushing.

Warnings

Use caution if you have used hot water immediately before performing this procedure because the water may be excessively hot when handling the purge port valves.

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