Tankless Water Heater Maintenance & Error Codes

Tankless water heater maintenance and plumbing service

Tankless Water Heater Maintenance & Error Codes

Tankless water heaters provide hot water on demand without the need for a bulky storage tank. While these systems are quite efficient and reliable, they still need routine maintenance. Mineral buildup, restricted water flow, venting problems, ignition issues, and other conditions can affect performance and trigger error codes.

No matter what brand of water heater you have, understanding basic maintenance requirements and common error codes can help you recognize problems early and know when to call a professional plumber.

Tankless Water Heaters

The Importance of Basic Tankless Water Heater Maintenance

Unlike traditional tank water heaters, tankless systems heat water as it passes through a heat exchanger. Over time, minerals such as calcium, magnesium, and lime can accumulate inside. This buildup can restrict water flow, reduce efficiency, and cause inconsistent water temperatures.

Most manufacturers recommend periodic maintenance, although the appropriate schedule depends on the model and local water conditions. In areas with hard water, your system may need more frequent flushing or descaling.

a tankless water heater after receiving maintenance in Idaho Falls by S&B Plumbing

Common Tankless Water Heater Maintenance Tasks

Flush and Descale the Heat Exchanger

Flushing removes mineral deposits that accumulate inside the heat exchanger and helps prevent clogs, and regular descaling helps maintain proper water flow and heat transfer.

You should follow manufacturer instructions when it comes to the exact flushing procedure and cleaning solution.

Clean the Water Inlet Filter

The inlet filter helps prevent debris from entering the water heater. A dirty or clogged filter can restrict water flow and affect performance. Just like your furnace or air conditioner, you should regularly inspect and clean the filter and replace it when necessary.

Inspect the Burner and Ignition Components

Gas tankless water heaters rely on proper combustion to heat water. A professional can inspect the burner, igniter, flame sensor, and related components for dirt, corrosion, or other problems.

Check Venting and Airflow

Blocked or improperly functioning intake and exhaust vents can lead to combustion problems and trigger error codes. You should check vent terminations for debris, cracks, snow, insects, or other obstructions.

Inspect Condensate Components

Condensing tankless water heaters produce condensate that must drain properly. Professional plumbers should inspect the condensate drain and neutralizer during routine service to make sure they are functioning correctly.

Check Safety Components

A professional maintenance visit may also include inspecting safety controls, temperature and pressure relief components, sensors, and other model-specific parts.

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Common Tankless Water Heater Error Codes

Navien

Navien error codes can vary by model, so you should always consult your owner’s manual. However, some commonly documented codes include:

E003 — Ignition failure

E110 — Exhaust or intake vent blockage

E438 — Clogged air intake filter

E012 — Flame loss during operation

E016 — Heat exchanger overheat

E109 — Combustion fan fault

E030 — Exhaust overheat

E004 — False Flame Signal

No matter what code you get, Navien documentation identifies it and provides model-specific diagnostic actions. For example, E003 may involve the gas supply or igniter, while E110 relates to exhaust venting.

Rinnai

Rinnai diagnostic codes can differ among product lines. Some frequently encountered codes include:

Code 10 — Air supply or exhaust blockage

Code 11 — Ignition/combustion problem

Code 12 — Flame failure

Code 14 — Overheating

Code LC — Lime or scale buildup

Rinnai documentation explains that an LC condition indicates mineral buildup in the heat exchanger, and Code 14 could mean something is overheating and needs further inspection.

Noritz

Noritz provides model-specific information for its tankless systems. Common codes include:

Error Code 11 — Ignition failure

Error Code 12 — Flame loss

Error Code 14 — Heat exchanger overheat

Error Code 16 — Abnormally high outlet water temperature

Error Code 20 — High-limit switch activated

Error Code 29 — Condensate drainage problem

Error Code 90 — Combustion abnormality

While Code 11 is a simple ignition failure, Code 90 is a combustion abnormality that may be associated with airflow, venting, gas pressure, or a dirty unit.

Rheem

Rheem error codes vary by model. A Rheem tankless manual lists several examples:

Code 1L — Lime buildup

Code 11 — Gas shut-off valve not fully open

Code 12 — Gas service interruption

Code 14 — Water heater overheating

Code 31 — Inlet thermistor problem

Code 33 — Outlet thermistor problem

Code 61 — Blower motor problem

Rheem recommends scheduling a professional evaluation for several of these conditions, especially if they involve overheating, sensors, or internal components.

Bosch

Bosch tankless water heaters use different codes depending on the model and generation. But some common codes include:

Error Code A7 — Hot water temperature sensor problem

Error Code A9 — Outlet temperature sensor not sensing the expected temperature

Error Code E0 — Internal software/hardware problem

Error Code E2 — Inlet temperature sensor problem

Bosch emphasizes that troubleshooting procedures are model-specific and that some issues require professional testing and service. You should consult your manual for system specifications.

Takagi

Takagi uses numeric error codes to help identify problems with ignition, combustion, sensors, valves, airflow, and other components.

Error Code 111 — Ignition failure

Error Code 121 — Loss of flame

Error Code 151 — Fan motor issue

Error Code 321 — Inlet thermistor failure

Error Code 331 — Mixing thermistor failure

Error Code 441 — Flow sensor failure

Error Code 510 — Gas valve failure/inadequate gas pressure or flow

Takagi recommends following the appropriate troubleshooting and service documentation for your specific model.

What Should You Do When an Error Code Appears?

An error code is a diagnostic message, not necessarily a complete diagnosis. A certain problem could have different causes depending on the model and installation.

If your tankless water heater displays an error code, you should write it down, check your owner’s manual for specifics, look for any obvious issues (like a blocked exterior vent), and contact a professional plumber if the code returns, the unit shuts down, or you have inconsistent hot water.

Do not bypass safety sensors or attempt repairs to gas, combustion, electrical, or internal components if you don’t have proper training.

The Five Most Common Problems We See

Most tankless water heater service calls S&B Plumbing receives involve one of these issues:

Dirty Air Intake Screen — Dust, pollen, cottonwood seeds, and debris can block airflow, causing air intake and combustion errors.

Heat Exchanger Scale Buildup — Hard water minerals can reduce efficiency and often trigger overheating errors.

Dirty Water Inlet Filter — Sediment can restrict water flow and reduces system performance.

Blocked Venting — Bird nests, leaves, insects, snow, or damaged vent piping can prevent proper airflow and force the system into a safety shutdown.

Dirty Flame Sensor — A dirty flame sensor may prevent the control board from confirming ignition, resulting in repeated startup failures.

Areas We Serve

Weber County

Davis County

Morgan County

Box Elder County

Salt Lake County

Schedule Annual Maintenance Today

Whether your tankless water heater needs a routine flush, intake screen cleaning, or diagnostics for an error code, our experienced technicians are ready to help.

Our regular maintenance keeps your system operating safely, efficiently, and reliably, helping you avoid many of the most common problems homeowners experience.

Contact S&B Plumbing in Marriott-Slaterville, Utah, today to schedule annual maintenance and enjoy dependable hot water all year long.