Tankless Water Heater Error Codes

What It Means
Rinnai Error Code 79 indicates a water leak inside your tankless water heater. This can be caused by condensation, a faulty heat exchanger, or other internal leaks. If left unaddressed, it can damage your unit and affect performance.

Symptoms You Might Notice

• Water pooling around the water heater

• Unexpected shutdowns or error codes appearing on the display

• Reduced hot water flow or intermittent heating

How to Solve Rinnai Error Code 79

1. Turn Off the Unit – Shut off both the gas and power supply to the water heater to prevent further damage.
2. Inspect for Leaks – Remove the front panel and carefully check for any signs of water, especially around the heat exchanger and water lines.
3. Dry the Unit – Use cloths, a vacuum, or a hairdryer to thoroughly dry the interior if water is present.
4. Check the Condensate Drain – Ensure the condensate drain line is clear and not clogged.
5. Reset the Unit – Try resetting the water heater by turning it off and on, or holding the reset button if your model has one.

When to Call a Professional
If the error persists after drying and resetting, the leak may be caused by a faulty sensor or a problem inside the heat exchanger. Call a licensed plumber experienced with Rinnai tankless water heaters to prevent further damage and ensure safe, reliable repairs.

What It Means
Navien Error Code E004 indicates a problem with flame detection, often caused by a blockage in the venting system or a leak in the heat exchanger. This error prevents the water heater from operating safely and can lead to intermittent hot water or unit shutdown.

Symptoms You Might Notice

• Water heater shuts down unexpectedly

• Error code E004 displayed on the control panel

• Reduced hot water output

• Strange noises or improper ignition

How to Solve Navien Error Code E004

1. Check the Venting System – Inspect for blockages such as debris or buildup that may interfere with proper airflow. Clear any obstructions.
2. Assess the Heat Exchanger – If the venting system is clear, the error may be caused by a leak or damage in the heat exchanger. A faulty heat exchanger typically requires professional replacement.
3. When to Call a Professional –Navien Error Code E004 can indicate serious internal problems. Call a licensed plumber experienced with Navien tankless water heaters to safely repair the heat exchanger or fix venting issues, ensuring your system operates efficiently and safely.

What It Means
Noritz Error Code 16 (EC16) occurs when the outlet water temperature rises to an abnormally high value. To protect your system, the water heater restricts water flow until the issue is resolved. Ignoring this error can reduce efficiency or damage internal components.

Symptoms You Might Notice

• Sudden spikes in hot water temperature

• Water flow restriction during operation

• Error code EC16 displayed on the control panel

• Unstable or inconsistent water temperature

Common Causes

• Mineral scale deposits in the heat exchanger or water components

• Improperly adjusted manifold pressures

• Incorrect gas type for the unit

How to Solve Noritz Error Code 16

• Reset the Unit – Unplug the water heater, wait 20 seconds, and plug it back in. This may temporarily clear the error.

• Professional Inspection – Most cases require a licensed plumber to descale the tankless water heater and check gas settings.

• Prevent Future Errors – Installing a water treatment system can help prevent scale buildup and reduce the likelihood of error codes like EC16.

When to Call a Professional
Because this error involves water temperature regulation and internal components, it’s best handled by a licensed plumber experienced with Noritz tankless water heaters. Call Tankless Water Heater Repair & Plumbing to safely restore your system and prevent recurring problems.

What It Means
Rheem Error Code 11 indicates an ignition failure or no ignition detected in your tankless water heater. This prevents the system from heating water properly and can lead to intermittent hot water or complete shutdown.

Symptoms You Might Notice

• Water heater fails to ignite

• Error code 11 displayed on the control panel

• No hot water or inconsistent water temperature

• Strange noises or repeated attempts to ignite

Common Causes

• Defective Ignition Components – Faulty igniter, gas valve, or flame sensor can trigger the error.

• Lack of Gas Supply – The unit requires a steady gas supply; any interruption can cause ignition failure.

• Blocked Venting – Obstructions in the vent can prevent proper combustion.

• Internal Leak – Leaks inside the unit can affect ignition and safety systems.

How to Solve Rheem Error Code 11
While some issues like checking gas supply may be straightforward, most causes require a licensed technician. Attempting DIY repairs can void your Rheem warranty or damage internal components.

When to Call a Professional
If you see Rheem Error Code 11, call a certified Rheem technician — like our team at Tankless Water Heater Repair & Plumbing — to safely diagnose and repair the system. Professional service ensures your warranty remains valid and your water heater operates reliably.

What It Means
Navien Error Code E003 (also called EC45) signals an ignition failure in your tankless water heater. This prevents the unit from heating water properly and may cause intermittent hot water or system shutdown.

Symptoms You Might Notice

• Water heater fails to ignite

• Error code E003 or EC45 displayed on the control panel

• No hot water or inconsistent water temperature

• Repeated ignition attempts or strange noises

Common Causes

• Gas or Power Issues – Gas supply valve may be closed, the cylinder may be empty, or the unit may not be properly connected to power.

• Ignition System Problems – Igniter, flame sensor, or air intake filter may be dirty, damaged, or worn. Wiring issues can also prevent proper ignition.

• Blocked Venting – Obstructions in the venting system can restrict airflow and cause ignition failure.

How to Solve Navien Error Code E003 / EC45

1. Check Gas and Power – Ensure the gas supply is fully open and the unit is correctly powered.
2. Inspect the Ignition System – Examine the igniter, flame sensor, and air intake filter; clean or replace components as needed. Check wiring connections.
3. Check Venting – Make sure vents are clear and unobstructed.
4. Potential Repairs – May include replacing the flame rod/igniter assembly, verifying gas pressure, or replacing the control board if necessary.

When to Call a Professional
Because ignition failures involve gas, electrical components, and safety systems, it’s best to contact a licensed technician. Call Tankless Water Heater Repair & Plumbing to safely diagnose and repair your Navien water heater and ensure reliable, safe operation.

What It Means
Noritz Error Code 45 (EC45) is specific to NRCP and CB models and indicates an internal water leak. The unit has a water leak sensor located at the bottom behind the circuit board. If enough water accumulates and trips the sensor, the error code will appear.

Symptoms You Might Notice

• Error code 45 displayed on the control panel

• Water pooling inside the unit or near the base

• Intermittent shutdowns or interrupted hot water

• Unusual sounds or moisture detected inside the unit

How to Solve Noritz Error Code 45

1. Dry the Sensor and Well – Carefully remove any moisture from the sensor area.
2. Inspect for Visible Leaks – Check for signs of leaking components or water lines. Replace any faulty parts found.
3. Consider Condensation – If no obvious leak is found, condensation from temperature differences may trigger the sensor.
4. Monitor for Reoccurrence – If the EC45 continues to appear, it’s likely an internal leak that requires professional assessment and repair.

When to Call a Professional
Internal leaks can damage the water heater and electrical components. Call a licensed plumber experienced with Noritz tankless water heaters to locate the leak, repair or replace affected components, and ensure your system is safe and reliable.

What It Means
Noritz Error Code 73 occurs when there is a problem with the circuit board settings in your tankless water heater. This can happen if a jumper connection or DIP switch is changed while the unit is powered, or if the circuit board is improperly programmed.

Symptoms You Might Notice

• Error code 73 displayed on the control panel

• Water heater fails to operate properly

• Intermittent hot water or shutdowns

• Unit does not respond to temperature adjustments

How to Solve Noritz Error Code 73

1. Power Cycle the Unit – Unplug the water heater for at least 30 seconds, then plug it back in. This may reset the error.
2. Avoid Changing Settings While Powered – Do not adjust jumper connections or DIP switches while the unit is turned on.

When to Call a Professional
If Error Code 73 persists after a reset, call a licensed contractor. A certified plumber or technician experienced with Noritz tankless water heaters can safely diagnose and repair the circuit board, restoring proper operation and protecting your unit from further damage.

What It Means
Noritz Error Code 90 indicates a combustion abnormality caused by an improper mixture of air and fuel. This prevents your tankless water heater from operating safely and efficiently.

Symptoms You Might Notice

• Error code 90 displayed on the control panel

• Water heater shuts down unexpectedly

• Reduced hot water flow or intermittent heating

• Unusual noises from the burner or fan

Common Causes

• Insufficient gas supply to the unit

• Blockage in the fuel vent

• Debris in the fan motor or air intake system

How to Solve Noritz Error Code 90
Because this error involves combustion, gas supply, and airflow, it requires a licensed professional. A technician will:

• Check gas pressures and fuel supply

• Inspect venting length and clear any obstructions

• Verify DIP switch settings and inspect the fan motor

When to Call a Professional
Do not attempt to fix combustion-related errors yourself. Call a licensed plumber or technician experienced with Noritz tankless water heaters to safely diagnose and repair Error Code 90, ensuring your system operates reliably and safely.

What It Means
Noritz Error Code 11 indicates an ignition failure in your tankless water heater. This means the unit is not firing up to heat water, which prevents your system from producing hot water.

Symptoms You Might Notice

• Water heater fails to ignite

• Error code 11 displayed on the control panel

• No hot water or intermittent hot water flow

• Strange startup noises or repeated ignition attempts

Common Causes

• Insufficient gas supply to the unit

• Insufficient airflow or blocked venting

• Debris or corrosion on the ignition plug

How to Solve Noritz Error Code 11

1. Check Gas Supply – Ensure the gas valve is fully open.
2. Inspect Venting – Make sure the exhaust vent is clear and unobstructed.
3. Examine the Ignition Plug – Ensure it is securely attached and free of debris.

When to Call a Professional
Because this error involves gas, airflow, and ignition components, it’s best handled by a licensed plumber or technician. Call Tankless Water Heater Repair & Plumbing to safely diagnose and repair your Noritz water heater and restore reliable hot water.

What It Means
Noritz Error Code 51 indicates a problem with the gas manifold, which could be caused by a component failure or water dripping onto the manifold. This can result in gas pressure issues and, if left unaddressed, potentially dangerous situations.

Symptoms You Might Notice

• Error code 51 displayed on the control panel

• Water heater fails to ignite or produces intermittent hot water

• Unusual smells or hissing noises near the gas manifold

• Reduced or inconsistent hot water flow

Common Causes

• Gas manifold failure

• Water intrusion onto the manifold

• Issues with the igniter or flame sensor

How to Solve Noritz Error Code 51

• Check Gas Supply – Ensure the gas line and valve are properly supplying fuel to the unit.

• Inspect Igniter and Flame Sensor – Clean or replace if faulty.

• Replace Gas Valve or Manifold – If the manifold is damaged or compromised, a licensed technician should replace it.

When to Call a Professional
Gas manifold problems involve safety risks and require professional handling. Call a licensed plumber or technician experienced with Noritz tankless water heaters to safely diagnose and repair Error Code 51.