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

Why is tankless maintenance so important? Can it really extend the life of a tankless water heater, increase efficiency, boost performance, and reduce common problems?

Here, you will find important information on maintaining a tankless water heater correctly, how often, and what components need to be cleaned, inspected, and taken care of.

How To Maintain A Tankless Water Heater: Things To Consider

While many people are saying that tankless water heaters are maintenance-free, that is simply not true. Also, I have found that some experts and websites, when talking about maintenance, suggest just cleaning the heat exchanger from the scale buildup.

Of course, there is much more than just cleaning a heat exchanger. If you leave other components unchecked, it could cause more stress on the system, element failure, no hot water, and a shorter lifespan.

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

How Tankless Water Heater Works

Anatomy of a tankless water heater
Tankless inside (photo:

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.

Check The Following While Tankless Is Operating

  • Inspect the burner flame inside the combustion chamber. You want to see the light blue flame with some yellow tips, and the flame should be stable – no flickering.
  • 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.

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.

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 do it at least twice a year, while if you are using a home water softener, you can flush the heater once every few years.

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 (available on 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.

How To Flush A Tankless Water Heater: Instructions

Flushing kit for tankless
  • 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 right 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, 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 The Following Components

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 – clean the burner 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 – 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.


Regular maintenance of the tankless water heaters is very much needed, especially descaling. The main reasons for flushing are due to the unit’s complexity, delicate components, frequent repairs, and higher service costs.

If you would like to see your tankless unit last as expected, which is over 20 years, perform as it should and fail much less, then you should take care of it as you would maintain your lovely vehicle.

Tankless maintenance should not be complicated for the DIY handyman, but if you need help, call a pro.

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