How to Maintain a Tankless Water Heater: DIY Instructions and Tips

Knowing how to maintain a tankless water heater is crucial for ensuring its efficiency and longevity. Regular upkeep, such as flushing to remove sediment buildup and inspecting components like the burner flame, helps prevent issues that could affect performance. Staying proactive with maintenance can avoid costly repairs and ensure your unit operates smoothly for years.

In this guide, you’ll find essential information on maintaining your tankless water heater, including how often maintenance should be done and which components need to be cleaned, inspected, and cared for.

While some people claim that tankless water heaters are maintenance-free, this is simply not true. Many experts and websites focus only on cleaning the heat exchanger to remove scale buildup. However, there’s much more to it. Neglecting other components can lead to system stress, element failure, no hot water, and a shorter lifespan.

Tankless water heater maintenance is recommended by all manufacturers and should be performed once or twice a year.

How Tankless Water Heater Works

Let’s first find out how tankless works and what the main components are:

• When the hot water faucet is open, it creates demand for hot water, and once the minimum water flow is met (detected by the flow sensor), the tankless kick in.
• While the cold water flows through the heat exchanger, the flow sensor, which detects the water flow, sends the signal to the computer board.
• The computer board then sends the signal to the gas valve to open and release the gas, while the flame rod generates sparks that ignite the gas burner.
• Water, which circulates through the heat exchanger, is then heated to the temperature set on the thermostat and moved to the point of service.
• The products of gas combustion or exhaust gases are removed through the venting system utilizing the electric fan (power vented). The venting system can use either concentric or dual-pipe systems.
• When the hot water tap is closed (no demand), the unit automatically shuts off.

This is how a non-condensing water heater works. There are also condensing models with one extra heat exchanger where water is preheated before entering the primary heat exchanger.

Note: The location of the tankless should allow easy access for the proper maintenance and service.

Basic Maintenance Tips

Safety First

Before you start any work (when required), it is important to follow some safety guidelines:

• Turn off the electrical supply on the main electric panel.
• Turn of the gas supply on the gas control valve.
• Close the water supply on the main shut-off valve.
• Make sure the inside water is not scalding hot before performing the maintenance.

Check the Following While Tankless Is Operating

• Inspect the burner flame inside the combustion chamber. The flame should be light blue with occasional yellow tips and remain stable without flickering. Yellow or red flames, smoke, or soot should not be present, as these are signs of potential issues.
• Check the relief valve by lifting and releasing the lever a few times. It should always go back to its normal, closed position. It should not leak any water when closed.
• Check the vent system that freely removes the exhaust gases without any leaks.

Notes: During the wintertime, it is normal to see white smoke coming out of the vents. Unusual sounds are often the sign that something is going on with the water heater.

How Often to Maintain a Tankless Water Heater

Maintenance frequency depends on your home location.

Depending on the water quality in your area, annual or bi-annual flushing is recommended. If water is hard, tankless is more prone to sediment buildup, so you should descale it at least twice a year, while if you are using a home water softener, you can flush the heater once every few years.

Tankless Water Heater Maintenance: Flushing for Extended Longevity

Flushing your tankless water heater is a crucial part of maintenance, especially if you live in an area with hard water.

What Is Hard Water?

Hard water contains minerals such as magnesium and calcium. While it is running through your tankless unit and the temperature of the water is higher, sediments can buildup on the heater’s elements, resulting in element failure, reduced water flow, or even blockage.

If you don’t maintain the heater and clean out deposits over time, mineral buildup can cause such damage that replacing it would be the only thing left.

Flushing Tips (Only if You Have Isolation Valves Installed)

Every tankless water heater should have isolation valves installed to allow easier servicing and maintenance.

In order to flush the tankless properly, you need approximately 3 gallons of white vinegar or any other delimer solution. Many experts suggest vinegar as a greener cleaning option than other commercial chemical delimers.

You also need a submersible pump to circulate the solution, a bucket, and a set of washer/dryer hoses. You can also buy a flushing kit.

Instructions

• Turn the gas off on the gas valve.
• Turn the power OFF.
• Close the cold inlet and open nearby hot water taps.
• Release the water from the tankless, and once the water stops, close the faucets.
• Check the water filter located within the cold inlet and below the heater. You can use a tiny brush to clean it.
• Put the submersible pump inside the bucket where you already poured home-grade vinegar.
• You need two hoses. Connect one end of the first hose to the submersible pump and the other end to the service ports of the isolation valve (cold side) installed on the water heater.
• Connect one end of the second hose to the service port (hot side) of the second isolation valve installed on the water heater and put the other free end into the bucket, making one continuous loop through which the vinegar will circulate.
• Open both valves of the isolation kit.
• Let it run for an hour to circle the vinegar through the tankless unit so it can remove deposits thoroughly.
• After flushing is over, you need to flush out vinegar residue.
• Turn off the pump, close the valve on the cold water side, and disconnect the hose.
• Open the cold water valve again and let the fresh water run through the unit for up to 2 minutes.
• Once done, close both valves (hot and cold). Remove the hose connected to the hot side.
• Clean the filter screen again. Make sure drain ports are closed.
• Open valves.
• Resume power.

Maintenance Checklist

As part of the yearly maintenance of your tankless water heater, the following should also be taken care of:

• Visually check if the water heater is operating correctly (no abnormal sounds, no flames blowing up, red/yellow flame, and no leaks).
• Make sure that all openings for combustion and venting are not blocked.
• Make sure there are no obstructions, damages, leaks, and corrosion in the venting system.
• Check if the burner flame has the proper color (blue flame) and shape.
• Proper work of the pressure relief valve is essential for safety.
• Locate a wire mesh filter installed inside the cold water inlet to clean it from debris.
• A gas burner should be checked annually for dust, dirt, grease, and lint accumulation.
• There should be no combustible materials, flammable vapor, and liquids nearby the water heater.
• Maintain the clearances recommended by the manufacturer from both combustible and non-combustible materials (applies to both indoor and outdoor units).
• Maintain the same diameter of a vent pipe for the full length starting from the water heater to the flue pipe termination.

Inspect and Clean Your Tankless Water Heater

Here are the components that should be inspected and cleaned regularly (as recommended by the manufacturer):

• Flow sensor – make sure there is no blockage and debris. Inspect the O-rings.
• Check that the filter on the cold water inlet is clean. Look for signs of mineral deposits.
• Gas burner and combustion chamber – clean both with the cleaning solution, and then wash it with runny water. After that, use the compressed air and wire brush. Also, inspect the gaskets and O-rings for any damages.
• Gas valve – verify that all gas connections are tight.
• Heat exchanger – clean the fins. Use compressed air to remove any soot and debris. Check the gasket. Inspect the element for any burnt marks, cracks, or hot spots.
• Flame sensor and ignition rod – inspect and clean if necessary. Use fine-grit sandpaper and a cloth to remove oxidation and deposits. Replace it if damaged or there are cracks in the ceramic housing. No sparks or weak sparks are signs when electrical connections of the igniter have to be cleaned.
• Inspect the computer board and wires for loose connection, breaks, and burn marks.
• Clean the fan and a cabinet. If you find any debris, make sure to check the gas burner and heat exchanger for obstructions. Use compressed air and blow it into the fan.

Maintenance Tips During Winter

In winter, especially during snowy or icy weather, ensure that snow or ice does not block the vent passages of your tankless water heater. Clear any obstructions promptly to maintain proper airflow.

If you plan to leave your home during cold weather and the water heater will be unused for an extended period, do not rely on antifreeze. Instead, drain the water from the unit to prevent freezing and potential damage.

After completing maintenance, thoroughly inspect the unit for any gas or water leaks. Remove all tools and cleaning materials used during the process, and ensure no combustible items, such as gasoline, are stored near the water heater.

If you encounter issues during or after maintenance—such as damaged components, abnormal sounds, or visible defects—do not attempt to repair the unit yourself. Immediately turn off the gas, electricity, and water supply, and contact a licensed technician for assistance.

Conclusion

Knowing how to maintain a tankless water heater—through descaling, flushing, cleaning, and regular checks—is essential for every homeowner. Proper maintenance reduces the need for repairs, lowers service costs, and extends the unit’s lifespan.

To ensure your tankless water heater lasts as expected—over 20 years, performs efficiently, and experiences fewer breakdowns—treat it with the same care you would give your vehicle.

While tankless maintenance is manageable for a DIY handyman, don’t hesitate to call a professional if you’re unsure or need assistance.