What E0 means

If your device displays E0, it indicates a communication problem between the humidity sensor and the main circuit board.

Common causes

• The humidity sensor connector on the circuit board is loose.
• The cable between the sensor and the circuit board is damaged or broken.
• The sensor has failed due to water exposure or physical damage.

What to try first

1. Locate the white 4-pin connector (humidity sensor socket) on the circuit board.
2. Unplug it fully, then plug it back in firmly.

If the error returns

If the connector is secure and the issue persists, the sensor and/or its cable may be defective. The typical solution is to replace the sensor. All of our units come with a complimentary sensor in the accessories box during the initial purchase. In extremely rare cases, if replacing the sensor does not solve the issue (and the user has verified that the pins were not connected backwards on the circuit board), the female connection on the circuit board or thermostat may be faulty.

Please note

Our units use dual sensors. The humidity sensor and the return-air temperature sensor are combined in a small gray plastic housing located at the lower left corner of the air filter. If the temperature sensor is faulty, it will display E2.

What E1 means

If your device displays E1, the system is detecting that the evaporator coil is getting too cold. On MSBA/MSWA units, a temperature sensor mounted on a copper tube at the evaporator monitors coil temperature.

Freeze protection

If the coil temperature drops below approximately 30°F (-1°C), the unit will shut the compressor off to help prevent freezing, and the display will show E1.

When it typically happens

• During Cooling mode
• During Dehumidify mode
• Most commonly when airflow is insufficient

What to check (airflow)

1. Confirm your ducting size is appropriate for your unit's BTU capacity.
2. Verify all vents and diffusers are fully open.
3. Make sure the return grille size is appropriate.
4. Check that filters are clean.
5. Inspect for any obstructions restricting airflow.

In many cases, restoring proper airflow will resolve the issue automatically.

Blower operation (multi-speed models)

When checking for airflow-related issues, blower operation should also be verified. Although this is rare, a blower that is not operating correctly on every speed can reduce airflow.

• If the blower is set to AUTO, the unit will switch between low, medium, and high speeds.
• If any individual speed does not operate correctly, airflow may drop when that speed is selected.
• This can contribute to airflow-related protection codes or shutdowns.

To verify, manually test the blower on each speed and confirm consistent airflow at every setting.

What E2 means

If your device displays E2, it indicates a communication problem between the return-air temperature sensor and the main circuit board.

Common causes

• The sensor connector on the circuit board is loose.
• The cable between the sensor and the circuit board is damaged or broken.
• The sensor has failed due to water exposure or physical damage.

What to try first

1. Locate the white 4-pin connector (sensor socket) on the circuit board.
2. Unplug it fully, then plug it back in firmly.

If the error returns

If the connector is secure and the issue persists, the sensor and/or its cable may be defective. The typical solution is to replace the sensor. All of our units come with a complimentary sensor in the accessories box during the initial purchase. In extremely rare cases, if replacing the sensor does not solve the issue (and the user has verified that the pins were not connected backwards on the circuit board), the female connection on the circuit board or thermostat may be faulty.

Please note

Our units use dual sensors. The humidity sensor and the return-air temperature sensor are combined in a small gray plastic housing located at the lower left corner of the air filter. If the humidity sensor is faulty, it will display E0.

What E3 means

If your device displays E3, the system is detecting a communication issue between the evaporator coil temperature sensor and the main circuit board.

Common causes

• The evaporator temperature sensor connector on the circuit board is loose.
• The cable between the sensor and the circuit board is damaged or broken.

What to check first

1. Locate the blue 2-pin connector for the evaporator temperature sensor on the circuit board.
2. Unplug it fully, then plug it back in firmly.

If the issue continues

If the connector is secure and the error persists, the evaporator temperature sensor and its cable may be defective. The corrective action is to replace the sensor with its cable.

Sensor location and access

The evaporator coil temperature sensor is mounted on the top copper tube of the evaporator coil. To access the sensor tip, remove the screws at the bottom of the compressor sound shield, then carefully separate the plastic panels.

What E4 means (Cooling / Dehumidifying Mode)

E4 is a high-pressure protection code. When high-side pressure exceeds approximately 550 PSI, the compressor will shut down to protect the unit and the controller will display E4.

Automatic reset behavior

• The controller will automatically reset once pressures return to normal.
• This automatic reset will occur up to two times.
• If it happens a third time, the controller will lock out and require a manual reset.

After correcting the issue, turn power OFF for at least 10 seconds and then restore power to clear the stored fault.

Cooling & dehumidifying mode - root cause

In cooling or dehumidifying mode, an E4 condition is caused by insufficient water flow. Reduced water flow prevents proper heat removal from the condenser, causing pressure to rise.

Correct water flow testing method

• Measure water flow using a 5-gallon bucket test.
• Measure at the outlet just before the thru-hull discharge.
• Measuring elsewhere may hide a restriction between the unit outlet and the thru-hull.

Most common causes of reduced water flow

• Blockages in the discharge hose or thru-hull
• Sand, shells, plant matter, or debris
• Partially clogged strainers

Required water flow values (measured at overboard)

• 6,000 BTU - 2.0 GPM (5-gallon container fills in ~120 seconds)
• 9,000 BTU - 3.0 GPM (5-gallon container fills in ~100 seconds)
• 11,000 BTU - 4.0 GPM (5-gallon container fills in ~75 seconds)
• 14,000 BTU - 4.6 GPM (5-gallon container fills in ~65 seconds)
• 16,000 BTU - 5.5 GPM (5-gallon container fills in ~55 seconds)

What E4 means (Heating Mode)

E4 is a high-pressure protection code. In heating mode, it occurs when system pressure rises above safe operating limits and the unit shuts down to protect itself.

Why E4 occurs during heating

• High water inlet temperature (above 70°F / 21°C)
• Insufficient airflow
• High thermostat set temperature

What to check (airflow)

• Confirm ducting size is appropriate for the BTU capacity of your unit
• Ensure all vents and diffusers are fully open
• Verify the return air grille size and placement are correct
• Check that filters are clean
• Inspect for any obstructions restricting airflow

Excessive water flow

Although less common, excessive water flow can contribute to high-pressure conditions during heating mode. If water flow is higher than required, install a ball valve flow reducer between the unit outlet and the thru-hull discharge.

What E5 means (Cooling / Dehumidifying Mode)

E5 indicates a low-pressure condition, meaning system pressure has dropped below normal operating levels.

Why timing matters

The meaning of an E5 condition depends on how quickly it appears after startup.

E5 appears immediately after startup

If E5 appears almost immediately after the unit starts, this indicates the system has lost refrigerant due to a leak. The unit must be inspected by a qualified technician to locate and repair the leak, evacuate the system, and properly recharge refrigerant.

E5 appears after 10 minutes or longer (Cooling / Dehumidifying)

If the unit runs for 10 minutes or longer before displaying E5 in cooling or dehumidifying mode, the cause is typically insufficient airflow.

What to check (airflow)

• Confirm ducting size is appropriate for the unit's BTU capacity
• Ensure all vents and diffusers are fully open
• Verify the return air grille size is correct
• Check that filters are clean
• Inspect for any obstructions restricting airflow

What E5 means (Heating Mode)

E5 indicates a low-pressure condition.

Why timing matters

The cause depends on how quickly the code appears after startup.

E5 appears immediately after startup

If E5 appears almost immediately after startup in heating mode, this typically indicates a loss of refrigerant. The unit should be inspected by a qualified technician to locate and repair the leak, evacuate the system, and properly recharge refrigerant.

E5 appears after 10 minutes or longer (Heating Mode)

If the unit runs for 10 minutes or longer before displaying E5 in heating mode, the most common cause is insufficient water flow.

What E7 means

E7 is related to the optional water flow switch feature on the control board. If a flow switch is installed and the system detects low or no water flow, the unit will shut down and display E7.

If you are NOT using a flow switch

If no flow switch is connected but the unit displays E7, verify that the FS terminals on the circuit board are properly jumped (bridged).

What E9 means

If your device displays E9, it indicates the evaporator coil temperature is too high. On MSBA/MSWA units, a temperature sensor mounted on a copper tube of the evaporator coil monitors coil temperature.

When E9 occurs

• Heating mode only
• Most commonly when airflow is insufficient

What EA means

If your device displays EA, it indicates a communication failure between the wall control panel (thermostat) and the main circuit board.

My thermostat will not light up

If the wall control panel (thermostat) does not power on, this is usually not a serious issue and rarely requires expensive parts. In most cases, the cause is a simple electrical protection event.

My unit is tripping the breaker

If your unit is tripping the breaker, this does not automatically mean the unit is defective. In most cases, the cause is related to breaker sizing, power supply conditions, or an external electrical issue.

There is a loud noise coming from the fan

Loud or unusual noise from the blower fan is usually caused by a mechanical issue, not an electrical fault. In most cases, you can identify the cause with a careful inspection.

My pump won't start

Step 1: Confirm the pump itself works

1. Turn power OFF.
2. Temporarily wire the pump directly to a proper power source (bypassing the unit) and test it.

• If the pump does not run, this indicates a pump issue.
• If the pump does run, continue below.

Step 2: Inspect the circuit board pump relay area

The most common unit-side cause is damage at the circuit board pump relay section. Many customers can see discoloration or smell a burned odor if the relay area has been damaged.

• If the board is visibly burned or damaged, it must be replaced.

Step 3: (Some serial numbers only) Redundant pump relay

On certain units, the primary pump relay connection is J06. A secondary connector J07 may be available next to it.

Prevent repeat damage

A burned pump relay is not caused by a manufacturing defect. It is almost always caused by an external condition. Verify the root cause before replacing the board.

1. Incorrect pump type / excessive amp draw (common). We recommend March pumps or MarinAire pumps.
2. Voltage surge or voltage drop.
3. Damaged pump wiring (pinched insulation, corrosion, loose connections, arcing).

Need help?

Contact support with your model number and serial number so we can confirm the correct next step.

There is a loud noise coming from the compressor

A loud noise that seems like it is coming from the compressor is very unusual. In most cases, the compressor is not the source of the noise.

Most common cause: vibration from tubing or coils

Customers often hear a loud vibration right as the compressor starts. This is usually caused by copper tubing or coil sections that have shifted slightly and are touching each other or touching the sound shield. When the compressor starts, the vibration transfers into the contact point and creates noise.

What to do

1. Turn power OFF.
2. Remove the compressor sound shield.
3. Inspect for any tubing or coil sections that are touching each other or contacting the shield.
4. Gently separate the contact point so there is a small gap and nothing can rub.

Less common: internal compressor damage from corrosion or contamination

On very old units with severe corrosion, a refrigerant leak can allow moisture contamination. If the compressor has been contaminated, it may become very loud and eventually fail to operate. This is not repairable in a practical way and is usually more cost-effective to resolve by replacing the unit.

If you hear humming or the compressor does not start

The most common cause is a low-voltage condition at the power source.

Voltage test (qualified electrician)

• 120V units: measure between PN and PL while the compressor is attempting to start
• 220V units: measure between PL1 and PL2 while the compressor is attempting to start

Voltage may look normal at rest but drop sharply during compressor start. This indicates a power source issue, not a unit defect.

Brand new unit behavior

If a brand new unit hums or trips the breaker at first start, this is not an indication of a defective compressor. Allow the unit to sit upright for 24 hours before operation. If needed, a temporary hard-start capacitor may be used once to assist initial startup and must be removed after successful startup.

Existing units: inspect compressor terminals

Remove the sound shield and inspect the wiring under the compressor terminal cover. In many cases, wires are burned, corroded, or loose. Replacing damaged wires typically resolves the issue.

Need assistance?

Contact support with your model number and serial number and describe the sound (a short video helps).

My thermostat is off by a few degrees

A small temperature difference is common and is often caused by sensor placement or the thermometer being used for comparison. Many consumer thermometers can read a few degrees differently when placed side-by-side.

Where temperature is measured

MarinAire units include a built-in temperature and humidity sensor located in front of the return air grille. Depending on the installation (especially if the unit is in an enclosed compartment), the return-air temperature can be noticeably different than the cabin temperature.

Use the included remote sensor for cabin measurement

Each unit includes a complimentary remote temperature sensor in the accessories package. If you want the system to measure temperature from the cabin area, you can connect the remote sensor instead of the built-in sensor.

How to switch to the remote sensor

1. Turn power OFF.
2. Locate the temperature/humidity sensor connector on the circuit board (the built-in sensor is already plugged in).
3. Disconnect the built-in sensor from the board.
4. Plug in the remote sensor to the same connector.
5. Place the remote sensor in the cabin away from direct discharge air, hot windows, or direct sunlight.

If the displayed temperature is wildly incorrect

• Verify the sensor connector is fully seated on the circuit board.
• Verify the sensor is not plugged in backwards (if applicable to your connector type).
• Inspect the sensor cable for damage.

App-only temperature issues (Neption smart Wi-Fi touchscreen)

If the thermostat display looks normal but the app shows an incorrect temperature, restart and reconnect the app. If the issue is only within the app, contact the app provider for assistance (Tuya / Smart Life).

Need help?

Contact support with your model number and serial number so we can confirm the correct sensor setup for your unit.