Tankless Water Heater
Maintenance Tips

How to maintain a tankless water heater? Extend the life of your tankless unit, reduce the operational costs and increase the efficiency following these simple inspection, cleaning, and flushing tips.

What you should know about regular and required tankless water heater maintenance and how it affects the heater's performance, efficiency, comfort, energy bill, property, and safety.

If you are the owner of the gas-powered water heater with on-demand heating, either condensing or non-condensing, use this article to find out if tankless maintenance is demanding, expensive, and beneficial, and what steps you should take for the proper care.

One of the greatest advantages of tankless is that every part can be replaced and that the unit can last for over 20 years, but only if it is adequately maintained. The recommendation from the manufacturers is to check and clean the complete water heating system once a year. Only a correctly maintained water heater would provide years of reliable and trouble-free operation.

Tankless water heaterTankless water heater

Before performing the maintenance

Maintenance should not be performed unless you do the following:

  • Unplug the electric cord which powers the water heater. You can also turn the unit OFF on the circuit breaker and electrical panel.
  • Use the manual gas valve to turn OFF the gas supply to the heater.
  • Turn the water supply OFF on the main shut-off valve. Most of the time, shut-off valves (or isolation valves) are installed so you can isolate the unit for service or flushing, for example.
  • Make sure the inside water is not scalding hot before performing the maintenance.

What needs to be checked and cleaned

Test a pressure relief valve

If the pressure inside the system has increased above allowed use the pressure relief valve to release the water and lower the pressure. To maintain proper operation, check the PRV once a year and test it by lifting and releasing the lever a few times. The lever should quickly go back into the closed position (should seat properly). After you open the valve, use the bucket to collect the discharged water but be careful as the water might be scalding hot.

Combustion chamber

Use the compressed air and dry cloth to remove the dust, debris, and dirt from the combustion chamber, heat exchanger, vents, fan, and motor.


When cleaning the vent system, make sure there are no obstructions and pipe defects. All vent connections should be tight and gaskets in good condition.

Water filter/sensor

Check also the water filter and remove the mineral deposits if needed. The flow sensor should preserve its capability to spin freely. If it doesn't turn properly, you can use the lemon juice to clean it, or if it doesn't fix the problem, replace it.


Locate the ignition rod and use the sandpaper (fine grit) to clean the tip of the rod to a bright finish. Be careful when cleaning the flame sensors to maintain the factory position.

You can use a shop vacuum to remove the small particles.

Sediment and limescale build-up

Most of the tankless water heaters are equipped with diagnostic tools to notify the owner when flushing is needed to remove the deposits. Hard water is the reason for deposits and limescale, especially inside the heat exchanger and copper coils as deposited minerals can disrupt the proper flow, even stop it over time. This will also shorten the unit's life and raise the energy bills.

Rinnai models, for example, will show codes such as LC1 or LC2. Use the descaling procedure or flushing to remove the sediment and limescale build-up.

It would help if you descaled your water heater at least once a year, but the frequency depends on the hardness of the water in your area. Find out how to descale the tankless water heater using this example.

Checking the flame color and pattern

All gas units are equipped with one or two gas burners. As part of the regular tankless water heater maintenance, visually inspect and check the burner flame for anything unusual.

The flame must burn clean with a blue and stable flame, not yellow, red, or burning with the smoke. Irregular combustion and flame patterns can cause smoke, soot build-up, and heat exchanger blockage. Also, check for cracks in the heat exchanger and flue gas spillage.

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Maintenance during the winter time

During the wintertime, especially when it is snowing or during icy cold weather, make sure that the snow or ice does not cover the vent passages.

If planning to leave during the cold weather, and if the water heater will be idle for some time, do not use the anti-freeze, but make sure to drain the water from the heater.

After you are done with the tankless water heater maintenance, always check for possible gas and water leaks. Remove all the tools and materials used in cleaning the unit and ensure that there are no combustible materials (such as gasoline) close to the unit.

If something goes wrong during or after the maintenance, there are damaged components, abnormal sounds during the operation, defects in the appearance, do not try to fix and repair the unit. Turn the gas, electricity, and water supply OFF and call the licensed technician.

How does the tankless work

It is essential for proper and easier maintenance to know how the tankless water heater works and what the components are.

As opposed to a conventional tank, a tankless water heater doesn't use a storage tank to store hot water. Water is heated directly inside the heat exchanger while it is flowing through. Some non-condensing models have one while condensing models utilize two heat exchangers (one for preheating and the second for central heating).

Most modern units are equipped with a microprocessor or electric board from where the whole operation is monitored and controlled. The flame rod (ignition electrode) generates the sparks and lights the flame on the gas burner and within the sealed combustion chamber. The products of combustion are vented out through the direct or power vented system.

For proper operation and safety, the units are equipped with several sensors and valves.

Tankless water heaters are great to have; they save space, provide unlimited hot water, heat on demand, can last over 20 years, but to keep them running well and smooth, and minimize the efficiency loss, professional installation and regular maintenance - as explained above, are required.

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