Tanked water heaters need regular upkeep, like draining the tank to descale the elements. But do tankless water heaters need maintenance? The short answer is yes. Everything electrical and mechanical needs servicing to keep it in working order.
We examine tankless water heater maintenance, including a checklist of what you should inspect as part of your service schedule.
Key Takeaways
- Necessity: Tankless water heaters require maintenance to prolong their lifespan and maintain efficiency.
- Frequency: Service your unit annually if you have hard water; soft water areas can wait every two to three years.
- Key Tasks: Essential maintenance includes flushing the system with vinegar, cleaning air filters, and clearing the water inlet screen.
- Cost: Professional servicing ranges from $45 to $200, though many tasks are DIY-friendly with a flushing kit.
Do Tankless Water Heaters Need Maintenance?
All mechanical and electrical appliances need maintenance to keep them running smoothly, and your tankless water heater is no exception. While they are often marketed as “low maintenance” compared to tanked units, they are not “no maintenance.”
Water carries minerals that coat the heater’s internal pipes and components over time. Calcium, magnesium, and iron create a chalky buildup known as scale. This scaling process stresses the heat exchanger, reduces efficiency, and eventually causes the heater to fail prematurely.
How Often to Service a Tankless Water Heater?
The frequency depends entirely on your water quality. If you live in a hard water area, your tankless water heater needs an annual service (flush) to prevent mineral buildup.
For those in soft water areas, you can likely wait every two to three years. However, preventative maintenance is always cheaper than replacing a heat exchanger.
How to Test Water Hardness
Knowing your water hardness level helps you determine your maintenance schedule. Here are three ways to check:
Homemade Soap Suds Test
You need a clear bottle with a cap and some pure liquid soap. Fill the bottle one-third full with tap water, add 10 drops of soap, and shake vigorously for 10 seconds.
If the soap foams up nicely and the water below remains clear, you have soft water. If the suds are thin and the water turns cloudy or milky, you likely have hard water.
Shop-Bought Testing Kit
When buying a test kit, ensure it specifically measures hardness (calcium/magnesium) rather than just pH or lead. Dip the strip into a water sample and compare the color change to the provided chart.
Speak to Your Municipal Water Company
Water utilities perform regular quality tests. Call them or check their website for the latest “Water Quality Report.” While this measures water at the treatment plant, it gives you a solid baseline for the hardness level in your neighborhood.
How Is Water Hardness Measured?
Water hardness measures calcium carbonate content in milligrams per liter (mg/L) or grains per gallon (GPG). Check your test results against the US Geological Survey’s scale:
| Water Hardness | Calcium Carbonate Level (Mg/L) |
| Soft water | 0 to 60 |
| Moderate water | 61 to 120 |
| Hard water | 121 to 180 |
| Extremely hard water | 180 plus |
Tankless Water Heater Maintenance Checklist
Servicing a tankless unit involves more than just a quick look-over. To keep your warranty valid and your water hot, focus on these critical components.
Descaling and Flushing
Whether you own a Navien or Rinnai tankless water heater, flushing the system is the most important task. This process removes the mineral deposits sticking to the heat exchanger.
Take Note
Tankless heaters hold very little water, so scale builds up faster than in tanked systems. Neglecting this leads to error codes and system failure.
To flush the system, you will need a submersible pump, a five-gallon bucket, and hoses. Follow these general steps:
- Isolate the power: Turn off the heater at the breaker or unplug it. Turn off the gas supply.
- Shut off water: Close the water inlet and outlet valves connected to the heater (usually part of a service valve kit).
- Connect hoses: Attach hoses to the service ports (drain valves) on the hot and cold lines. Place the pump in the bucket.
- Add solution: Fill the bucket with 3 to 4 gallons of undiluted white vinegar. Connect the cold water hose to the pump.
- Circulate: Open the service valves and turn on the pump. Let the vinegar circulate through the heater for 45 to 60 minutes. This dissolves the scale.
- Rinse: Turn off the pump, dump the vinegar, and flush fresh water through the heater for 5 minutes to remove any residue.
- Restart: Close service valves, disconnect hoses, open the main water supply, and turn the power/gas back on.
Cleaning the Inlet Water Filter
Most tankless units have a small screen filter on the cold water inlet. This catches large debris, sediment, and rust particles before they enter the unit.
- Locate it: It is usually found where the cold water line enters the unit.
- Clean it: After isolating the water supply, unscrew the small filter plug, remove the screen, and rinse it under a tap. If it is damaged, replace it.
Cleaning the Air Intake Filter
Gas tankless heaters need fresh air for combustion. If the air intake filter gets clogged with lint, dust, or pet hair, the unit will suffocate and lose efficiency.
- Inspect it: Open the front panel (consult your manual) to find the air intake filter mesh.
- Wash it: Remove the filter and wash it with mild soap and water. Dry it completely before reinserting it.
Igniters and Sensors
Old-school heaters used pilot lights, but modern tankless units usually use electronic igniters and flame rods. If these get dirty with carbon buildup, the heater may fail to light.
- Check the rods: If you are comfortable opening the combustion chamber, inspect the flame rod for white or black residue.
- Clean gently: Use a dollar bill or very fine sandpaper to gently clean the metal rod. Do not use standard sandpaper or wire brushes, as these can damage the sensor.
Cost to Service a Tankless Water Heater
If you prefer not to DIY, you should hire a professional plumber. Many installers offer annual maintenance plans.
The average cost to service a tankless water heater ranges from $45 to $200. A simple inspection is on the lower end, while a full descaling flush typically costs between $150 and $200. Considering a new heat exchanger costs hundreds of dollars, this annual fee is a smart investment.
When to Replace a Tankless Water Heater
With proper maintenance, tankless water heaters can last 20 years or more. However, nothing lasts forever. Watch for these signs that it might be time to retire your unit.
Loud Rumbling Noises
If your heater sounds like rocks are tumbling inside it, you likely have severe scale buildup. This sound, often called “kettling,” indicates the heat exchanger is overheating. If a flush doesn’t fix it, the internal damage may be irreversible.
Age of the Unit
If your unit is approaching the 20-year mark and requires frequent repairs, it is likely time to upgrade. Newer models are more efficient and have better safety features.
Rising Energy Bills
A heater coated in scale has to work much harder to heat water. The US Department of Energy notes that tankless systems are highly efficient, but this efficiency drops as the unit ages and gets dirty. If your gas or electric bill spikes without a change in usage, your heater is the likely culprit.
Cost of Repairs vs. Replacement
Use the 50% rule: If a repair costs more than 50% of the price of a new unit, replace it. Technology improves rapidly, and a new unit will come with a fresh warranty.
FAQs
Can You Maintain a Tankless Water Heater Yourself?
Yes, homeowners can perform basic maintenance like flushing with vinegar and cleaning air filters. However, if you are uncomfortable working with gas lines or high-voltage electricity, hire a professional to ensure safety.
What Happens If You Don’t Flush Your Tankless Water Heater?
Minerals will build up on the heating elements, leading to reduced water pressure, longer wait times for hot water, loud noises, and eventually a cracked heat exchanger.
How Often Should You Replace Your Tankless Water Heater Filter?
The cold water inlet filter does not usually need replacing unless it is torn or damaged; it just needs to be removed and rinsed clean annually.
Can I Use Chemical Descalers Instead of Vinegar?
Yes, commercial descaling solutions are available and effective. However, plain white distilled vinegar is food-safe, inexpensive, and generally recommended by manufacturers for safe home maintenance.
Show Your Tankless Water Heater Some Love
Do tankless water heaters require maintenance? Absolutely. While they are durable workhorses, they are not invincible against hard water and debris.
Treat your heater to an annual flush and filter clean. A little TLC keeps the hot water flowing endlessly and saves you from a freezing cold shower surprise down the road.
