Troubleshooting Noritz Error Code 59: What It Means & How to Fix

A Noritz Error 59 indicates a **Combustion Air Supply Error**. This specific fault code is triggered when the water heater’s control board detects that the combustion fan motor is not rotating at the correct RPM (Revolutions Per Minute) or the fan signal is not being communicated back to the circuit board accurately.

If you are seeing this code, you are likely experiencing a total lack of hot water, as the unit will lockout for safety. You might hear the fan attempt to spin up with a faint humming or clicking sound, followed quickly by the unit shutting down. While a “combustion error” sounds intimidating, it is often caused by debris or component wear that can be addressed with the right technical approach. Don’t worry; with a methodical inspection, this is a fixable issue that often doesn’t require a total unit replacement.

How to Fix Noritz Error 59 (Step-by-Step)

Follow these steps carefully. If at any point you feel uncomfortable working with electrical components, contact a licensed technician.

1. Safety First – Power and Gas Shutdown:

   Before opening the unit, turn off the electrical power by unplugging the unit or switching off the dedicated breaker. Close the gas shut-off valve located on the yellow gas line leading into the unit. WARNING: Working on a powered unit can result in severe electrical shock or short-circuiting the expensive control board.

2. Remove the Front Cover:

   Use your Phillips head screwdriver to remove the four screws (usually located at the corners) holding the front panel in place. Carefully pull the panel toward you and set it aside in a safe place to avoid scratching the finish.

3. Inspect the Air Intake Filter:

   Locate the air intake filter, usually found at the top or side of the internal cabinet. Pull the filter out and inspect it for heavy dust or debris. Wash it with mild soap and water, dry it completely, and reinstall it. A clogged filter is the #1 cause of “starving” the fan of air.

4. Examine the Combustion Fan:

   The fan is typically located at the bottom of the unit. Check the wiring harness leading from the fan to the circuit board. Ensure all plastic connectors are seated firmly and that no wires are frayed or pinched. Use a can of compressed air to blow out any dust from the fan housing and the motor’s cooling vents.

5. Perform a Multimeter Test (Advanced):

   Turn the power back on (be extremely careful with the open cabinet). Set your multimeter to DC Voltage. Locate the wire harness for the fan. Test the voltage between the red and black wires (power) and the white/yellow wires (signal). You should see a voltage increase as the unit attempts to start. If the board is sending power but the fan isn’t spinning, the Fan Motor is defective. If no power is leaving the board, the PCB is likely the culprit.

6. Clear the Error Code (The Reset):

   Once you have cleaned the components or replaced a part, turn the power off for 30 seconds, then back on. Open a hot water faucet fully to trigger a “demand” for heat. The unit should initialize, the fan should ramp up, and the Error 59 should disappear.

Detailed Diagnosis: Root Causes

To fix Error 59, you must understand the mechanical and electrical relationship between the fan and the control board. Here are the primary reasons this system fails:

1. Accumulated Debris and Dust (Most Common): Tankless water heaters pull in a significant amount of air. Over time, dust, pet hair, or lint can coat the fan blades. Because these fans are balanced with extreme precision, even a small amount of weight on the blades can reduce the RPM below the threshold required by the PCB. This “drag” causes the motor to draw more current, triggering the error.
2. Fan Motor Bearing Failure: The combustion fan uses high-speed bearings designed for years of service. However, if the unit is installed in a humid environment or near corrosive chemicals (like laundry detergent in a basement), the bearings can seize or develop friction. This physical resistance prevents the motor from reaching the target speed dictated by the water flow rate.
3. Circuit Board (PCB) Communication Fault: The fan communicates with the PCB via a “Hall Effect” sensor. This sensor sends a pulse signal back to the board for every revolution. If the PCB has a failed capacitor or a “cold” solder joint in the fan control circuit, it may misinterpret the fan’s speed or fail to send the 120V AC (or DC, depending on the model) required to spin the motor.
4. Ventilation Blockage: While Error 59 is usually internal, a significant blockage in the intake or exhaust piping can create “backpressure.” This backpressure acts as a physical brake on the fan, making it work harder and spin slower than the control board expects for that specific power input.

Symptoms of Noritz Error 59

When your Noritz tankless water heater encounters an Error 59, the system behaves in a very specific manner to prevent unsafe combustion levels. You will notice the following physical and operational signs:

• The Digital Display Flashes “59”: The most obvious sign is the remote controller or the internal circuit board LED display blinking the number 59 repeatedly.
• Sudden Temperature Drop: If the error occurs during use, the water will transition from hot to cold almost instantly as the gas valves are shut off for safety.
• Audible Fan Struggle: You may hear the combustion fan attempting to start. This might sound like a low-pitched hum, a vibrating “flutter,” or a grinding noise if the bearings are failing.
• Repeated Ignition Failure: The unit may click several times as the igniter attempts to fire, but because the fan cannot provide the necessary air-fuel mixture, the system aborts the process.
• Air Flow Obstruction: In some cases, you might notice the exterior exhaust vent smells strongly of gas or appears to have less “force” behind the air being pushed out.

How to Prevent Error 59

Once you have cleared the error, proactive maintenance is the only way to ensure it doesn’t return during a cold winter morning.

• Annual Intake Cleaning: Make it a habit to check the air intake filter every 6 to 12 months. If you live in a dusty area or have pets that shed, check it every 3 months. Keeping the airflow “lean and clean” reduces the mechanical stress on the fan motor.
• Install a Power Surge Protector: The control boards on Noritz units are sensitive to voltage spikes. A surge can damage the fan’s RPM-sensing circuit. Use a high-quality surge protector designed specifically for tankless water heaters to stabilize the incoming power.
• Maintain Clear Exhaust Vents: Periodically walk outside and check the termination points of your exhaust and intake pipes. Ensure no bird nests, beehives, or snow drifts are obstructing the pipes, as backpressure is a silent killer of combustion fans.

Frequently Asked Questions (FAQ)

Q: Can I just bypass the fan sensor to get hot water temporarily?
A: Absolutely not. The fan sensor is a critical safety component. If the fan isn’t spinning at the right speed, the gas-to-air ratio will be incorrect, which can lead to incomplete combustion and the production of Carbon Monoxide (CO). Never bypass safety sensors on a gas appliance.

Q: My fan spins, but I still get Error 59. Why?
A: This usually points to the “Hall Effect” sensor inside the motor or the communication circuit on the PCB. Even if the fan is physically moving, if the control board cannot verify the exact RPM, it will throw Error 59 as a fail-safe. In this scenario, testing with a multimeter is the only way to determine if the motor signal or the board’s receiver is at fault.

Q: Is it worth replacing the fan motor on an older Noritz unit?
A: Generally, yes. A replacement fan motor usually costs between $150 and $250. Given that a new Noritz unit can cost $1,200 to $2,000 plus installation, replacing the fan is a cost-effective way to extend the life of your heater, provided the heat exchanger is still in good condition.