Bionaire B700 Temperature Sensor Faulty, How to Repair

The Bionaire B700 is a popular climate‑control appliance that keeps indoor air at an ideal level of humidity and temperature. Users love its quiet operation and efficient water‑to‑air conversion. Over time, however, one component that can give way is the temperature sensor. When the sensor fails, the unit may display error codes, stop heating, or simply fail to respond to temperature settings.

This guide walks you through diagnosing a faulty temperature sensor, safely opening the humidifier, replacing the sensor, and re‑testing the system. It is written as a step‑by‑step tutorial with clear explanations, safety reminders, and practical tips.

Understanding the Temperature Sensor Problem

Common Symptoms

• Error Code Display: The LED panel may flash “T‑SENS” or show a red triangle, indicating a temperature sensor fault.
• No Temperature Change: Even when the temperature setting is adjusted, the device fails to warm or cool the air.
• Unresponsive Heater: The heating element turns on and off erratically or not at all.
• Excessive Heat or Cold: The unit may run too hot or too cold, causing discomfort or even damage to surrounding surfaces.

Why the Sensor Fails

The sensor is a small thermistor mounted near the heating element. It can degrade due to:

• Repeated thermal cycling (heat‑cool cycles).
• Exposure to high humidity or water vapor.
• Age and wear of the internal circuitry.
• Dust or debris blocking the sensor’s connection.

Tools and Materials Needed

You can usually find the replacement sensor from the Bionaire parts catalog or from reputable electronics suppliers. Make sure it matches the model number and is rated for the same voltage and temperature range.

Safety Precautions

1. Unplug the Unit – Disconnect the humidifier from the mains before touching any internal parts.
2. Avoid Contact with Water – The device contains a water reservoir; ensure it is empty or sealed to prevent spillage.
3. Use an Anti‑Static Wrist Strap – Static electricity can damage the microcontroller that reads the sensor.
4. Work on a Stable, Clean Surface – Keep tools and parts organized to avoid dropping them.
5. Follow Manufacturer’s Warranty – If the unit is still under warranty, consider contacting Bionaire customer support before opening it.

Step‑by‑Step Repair Procedure

1. Prepare the Work Area

• Place the humidifier on a flat table.
• Remove any objects around it that might interfere with the opening process.
• Verify that the power cord is not plugged in.

2. Remove the Front Cover

1. Locate the Plastic Latches – The B700’s front panel is held by a set of plastic clips along the sides and bottom.
2. Use the Flathead Screwdriver – Insert the screwdriver into a latch slot and gently pry.
3. Slide the Panel Forward – Once all latches are released, carefully lift the panel off.
4. Set Aside the Panel – Keep it in a safe place so it doesn’t get lost.

3. Identify the Temperature Sensor

• The sensor sits directly above the heating element and below the thermostat circuit board.
• It looks like a small metal or plastic cylinder with a wire connected to it.
• Trace the wire to the main board where it plugs into a small pin.

4. Inspect the Sensor and Wiring

• Visual Check – Look for cracks, burn marks, or corrosion on the sensor body and wire.
• Clean the Connections – Use a brush or compressed air to remove dust from the sensor and its socket.
• Test with a Multimeter – If you have one, measure resistance across the sensor’s leads. A faulty sensor will often show infinite or extremely high resistance.

5. Disconnect the Old Sensor

1. Unscrew the Mounting Screws – The sensor is usually secured with two small screws.
2. Pull the Wire – Gently wiggle the wire to break the connection from the board.
3. Remove the Sensor – Lift it out of its cradle.

6. Install the New Sensor

1. Position the Sensor – Place the new sensor in the same location as the old one.
2. Screw It In – Tighten the mounting screws just enough to hold it firmly but avoid over‑tightening, which could damage the plastic housing.
3. Reconnect the Wire – Insert the wire into the board’s pin and secure it with a small clamp or solder, depending on the original design.

7. Reassemble the Unit

1. Attach the Front Cover – Align the panel with the latches.
2. Snap It Into Place – Press firmly until the plastic clips click back into position.
3. Check All Screws – Ensure no screws or panels are loose.

8. Power On and Test

1. Plug the Unit Back In – Connect the power cord to a grounded outlet.
2. Set a Temperature – Use the control panel to set a desired temperature.
3. Observe the LED – The error code should disappear, and the unit should begin heating or cooling as commanded.
4. Monitor Performance – Run the unit for a few minutes to confirm stable operation and that the sensor responds correctly to changes.

Post‑Repair Checklist

• Verify No Error Codes – The display should be clear of any fault indicators.
• Check Temperature Accuracy – Use a separate thermometer to compare the ambient temperature against the humidifier’s readings.
• Confirm Smooth Operation – The fan and heating element should cycle normally.
• Inspect for Leaks – Ensure the water reservoir is sealed and no moisture is leaking from the sensor area.

Common Troubleshooting Scenarios

If problems continue after a sensor replacement, it may be time to contact Bionaire support or a licensed appliance repair technician.

Preventive Maintenance Tips

• Clean the Water Reservoir Regularly – Lime scale and mineral buildup can affect sensor accuracy.
• Inspect Wiring Periodically – Look for frayed or cracked wires that could lead to sensor failure.
• Keep the Unit Dry – Avoid prolonged exposure to high humidity or water spillage.
• Use Filtered Water – Hard water accelerates wear on the heating element and sensor.
• Schedule Professional Checks – If you use the humidifier extensively, consider a yearly professional inspection.

Frequently Asked Questions

How long does a replacement sensor last?

Typically, a new sensor can last anywhere from 2 to 5 years, depending on usage frequency and environmental conditions.

Can I test the sensor before purchasing a replacement?

Yes, if you have a multimeter, you can check the resistance of the old sensor to confirm it is indeed faulty before buying a new one.

Is it safe to perform this repair myself?

If you follow all safety precautions, unplug the unit, and use the correct tools, it is safe. However, if you feel uncomfortable, call a professional.

What if the sensor is integrated into the main board and cannot be removed?

In some models, the sensor is soldered to the PCB. In that case, replacing it requires a soldering kit and advanced skills. It is usually more cost‑effective to replace the entire control board or contact Bionaire support.

Will a faulty sensor affect the water reservoir or other components?

A faulty temperature sensor mainly impacts temperature regulation. It will not directly damage the reservoir, but incorrect temperature readings can lead to over‑heating or under‑heating, potentially stressing the heating element over time.

Final Thoughts

A malfunctioning temperature sensor can render a Bionaire B700 useless or cause discomfort at home. By following the steps outlined above, you can safely diagnose and replace the sensor, restoring reliable performance.

Remember to keep the unit clean, use filtered water, and perform routine checks to prolong the life of the sensor and other components. If the problem persists after a replacement, consider reaching out to Bionaire’s customer service or a licensed appliance repair specialist.