Your tankless water heater is a marvel of engineering. It heats water on demand, saves energy, and takes up almost no space. But like any precision machine, it needs care. Neglect it, and that endless hot shower becomes a cold, frustrating trickle.
The good news? Maintaining a tankless water heater is straightforward. You dont need to be a plumber. You just need a plan and a few basic tools. This guide walks you through everything from descaling to winterizing, so your unit keeps performing for years.
Why Regular Maintenance Matters for Your Tankless Water Heater
Think of your tankless water heater like a high-performance sports car. It works hard. Every time you turn on a tap, water rushes through a heat exchanger made of copper or stainless steel. This is where the magic happens. There is more on anode rod replacement tips in a guide of its own.
But hard water has other plans. Minerals like calcium and magnesium love to stick to hot surfaces. Over time, this sediment buildup acts like an insulator. It forces the burner to work harder and longer to heat the water. Your energy bills go up. Water temperature fluctuates. Eventually, the heat exchanger can fail completely.
Skipping maintenance voids warranties on many units from brands like Rinnai and Navien. Most manufacturers require annual descaling to keep the warranty valid. Thats a costly mistake to avoid.
Regular care gives you three things:
- Reliability: No surprise cold showers on a winter morning.
- Efficiency: Lower gas or electric bills.
- Longevity: A unit that lasts 20 years instead of 10.
How to Flush and Descale Your Tankless Water Heater (Step-by-Step)
This is the single most important maintenance task. It removes the mineral scale that builds up inside the heat exchanger. For this project, many professionals recommend using the EcoSmart ECO 11 tankless electric water heater for smaller applications, but the flushing process is similar for all brands.
You should do this at least once a year. If you have very hard water (above 7 grains per gallon), do it every six months.
What You’ll Need
- Two 5-gallon buckets
- A submersible pump (a small utility pump or a dedicated tankless flushing kit)
- Two washing machine hoses (or similar reinforced hoses)
- White vinegar (at least 2 gallons) or a professional descaling solution
- A flathead screwdriver
- Adjustable wrench
- Shop towels or rags
The Step-by-Step Process
- Turn off the power. For electric units, flip the breaker. For gas units, turn the gas valve to “Off” and disconnect the power cord.
- Close the water shut-off valves. There are two: one on the hot water line, one on the cold. Turn them clockwise.
- Open a hot water tap. This relieves pressure in the system. Let it run until water stops flowing.
- Disconnect the service ports. Your unit has two brass valves with caps. They are usually labeled “Service In” and “Service Out.” Unscrew the caps.
- Connect the hoses. Attach one hose to the cold water service port. Put the other end in your bucket. Attach the second hose to the hot water service port. Put its other end in the pump.
- Fill the bucket. Pour 4 gallons of white vinegar into the bucket. Make sure the pump is fully submerged.
- Start the pump. Plug in the pump. The vinegar will circulate through the heat exchanger. Let it run for 45 to 60 minutes.
- Flush with clean water. After descaling, disconnect the pump. Run a garden hose through the cold water service port for 5 minutes to flush out all vinegar and loosened debris.
- Reconnect everything. Remove the hoses, reattach the service port caps, and open the shut-off valves.
- Restore power. Turn the breaker or gas valve back on. Open a hot water tap to purge air from the system.
Pro tip: A dedicated tankless water heater descaling kit comes with all the hoses and a pump. It saves you the hassle of finding individual parts.
How to Clean Your Tankless Water Heaters Air Filter and Inlet Screen
While descaling handles the inside, the outside needs attention too. Your unit breathes air and drinks water. Both need to be clean.
Cleaning the Air Filter
Gas tankless units have an air filter on the bottom or side. It prevents lint, dust, and pet hair from entering the combustion chamber. There is more on benefits of tankless water heating in a guide of its own.
- Remove the filter cover (usually snaps off).
- Pull out the filter.
- Vacuum it gently with a brush attachment.
- If its greasy, wash it with mild soap and water. Let it dry completely before reinstalling.
Do this every three months. A clogged air filter causes bad combustion, soot, and system shutdowns.
Cleaning the Inlet Water Screen
The cold water inlet has a small mesh screen. It catches debris from your pipes. If it clogs, you get low flow or error codes.
- Turn off water and power.
- Unscrew the union fitting on the cold water inlet pipe.
- Pull out the screen with needle-nose pliers.
- Rinse it under running water. Use an old toothbrush if its caked with sediment.
- Reinsert the screen and tighten the fitting.
Troubleshooting Common Tankless Water Heater Error Codes
Your unit talks to you. It just uses numbers. Knowing common error codes can save you a service call.
| Error Code | Common Cause | Quick Fix |
|---|---|---|
| Error Code 11 | Ignition failure (gas unit) | Check gas supply is on. Reset the unit. |
| Error Code 12 | Thermistor or overheating issue | This often indicates scale buildup. Perform a tankless water heater vinegar flush immediately. |
| Error Code 16 | Outlet thermistor issue | Check for air in the lines. Purge by opening a hot tap. |
| Error Code 29 | Gas solenoid valve issue | Turn unit off for 60 seconds, then restart. If persistent, call a pro. |
| Error Code 99 | Fan motor issue (gas unit) | Check the air filter. Clean or replace it. |
For a tankless water heater error code 12 fix, the solution is almost always descaling. The heat exchanger is overheating because scale prevents water from absorbing the heat. Don’t ignore this one.
How to Winterize Your Tankless Water Heater (and Prevent Freeze Damage)
If you live in a cold climate, winterizing is non-negotiable. A frozen heat exchanger can crack, costing you a thousand dollars to replace.
For a Unit in an Unheated Space (Garage, Cabin, Vacation Home)
- Turn off power and gas.
- Close the gas valve.
- Shut off the cold water supply valve.
- Open all hot water taps in the house to drain the system.
- Remove the drain plug on the bottom of the unit (check your manual for location).
- Disconnect the inlet and outlet pipes to allow any trapped water to escape.
- Blow compressed air through the heat exchanger to remove residual water.
- Leave the service port caps off to allow airflow.
For Units with Built-In Freeze Protection
Modern units from brands like Takagi and Navien have electric heaters that keep the internal temperature above freezing.
- Keep the unit plugged in (even if you turn off the water heater).
- Do not turn off the circuit breaker for this outlet.
- Ensure the room temperature stays above 32F (0C).
Critical warning: Never use antifreeze in a tankless water heater. It will damage the heat exchanger and void the warranty.
A Quick Maintenance Checklist
Print this and stick it on your unit.
- Monthly: Check for error codes. Listen for unusual noises.
- Quarterly: Clean the air filter.
- Annually: Perform a full tankless water heater cleaning (descaling flush).
- Before Winter: Winterize if unit is in an unheated space.
Your tankless water heater is an investment. A little routine care goes a long way. Follow this tankless water heater maintenance checklist, and youll enjoy endless hot water without endless repairs. If you are considering an upgrade or a new installation, check out our guide on the best electric tankless water heater for shower to find the right fit for your home. For apartment dwellers, the EcoSmart ECO 11 tankless electric water heater apartment shower performance is a popular choice.
For a deeper dive into professional-grade maintenance techniques, the hot water service handbook is an excellent resource for technicians and homeowners alike.
Now go give your water heater the care it deserves. Your next hot shower will thank you.
