mysa makes a quiet but annoying buzzing sound, only when the heat is on. is this normal?

Diagnosis

The buzzing sound you are hearing is an audible manifestation of electrical vibration, specifically originating from the internal relay or the terminal connections. Because the Mysa is designed for high-voltage electric baseboard heaters (typically 120V or 240V), it uses a mechanical relay to switch the heavy current load. When the relay is engaged to provide heat, the electromagnetic coil creates a magnetic field; if there is a loose connection or a slight mechanical misalignment, this energy manifests as a 60Hz hum or a rapid "chatter." This is not considered "normal" operation, although it is common in installations where the wiring is not fully seated. You can confirm the source by placing your ear close to the unit while the heat kicks in. If the sound is a sharp, crackling buzz, it is likely micro-arcing at the terminal. If it is a steady, low-frequency hum, it is likely the relay vibrating against the plastic housing or a loose wire vibrating against the terminal plate. This can lead to heat buildup at the connection point, which may eventually degrade the wire insulation or damage the thermostat's internal circuitry.

How to Fix It

To resolve the buzzing, you must ensure a high-torque, secure connection at the high-voltage terminals. Follow these exact steps:

1. Locate your electrical panel and switch off the circuit breaker dedicated to the heating zone. Use a non-contact voltage tester on the Mysa wires to verify that no current is flowing before proceeding.
2. Gently pull the Mysa faceplate away from the wall mounting plate. Be careful not to tug on the wires.
3. Inspect the three primary connection points: the Line (L), the Load (1), and the Neutral (N). Look for any signs of discoloration or "pitting" on the copper wire ends.
4. Using a precision Phillips head screwdriver, tighten the terminal screws. The wire should be clamped firmly; give each wire a gentle "tug test" to ensure it does not slide.
5. If the wire is stranded rather than solid core, ensure the strands are twisted tightly and not splayed out, as stray strands can cause vibration and electrical noise.
6. Check that the mounting plate is screwed flush against the drywall. If the plate is bowed or loose, the relay's vibration can resonate through the wall, amplifying the sound. Tighten the mounting screws until the plate is perfectly flat.
7. Snap the faceplate back into position and restore power at the breaker.

If That Didn't Work

• Check for Circuit Overload: If the buzzing persists, verify that the total wattage of the heaters on that circuit does not exceed the Mysa's maximum rating (typically 3000W). An overloaded circuit can cause the relay to struggle and vibrate more intensely under the heavy current draw.
• Inspect for Wire Gauge Mismatch: Ensure you are using 12 AWG or 14 AWG copper wire. If the wire is too thin, it may not seat properly in the terminal block, leading to a loose fit that vibrates during operation. You may need to strip an additional 1/4 inch of insulation to ensure the clamp is gripping the metal, not the plastic coating.
• Isolate Wall Resonance: If the hum is coming from the wall itself, place a thin piece of non-conductive rubber or a foam gasket between the mounting plate and the drywall. This dampens the mechanical vibration of the relay and prevents the wall from acting as a sounding board.
• Request a Hardware Replacement: If the buzzing is a high-pitched "whine" rather than a low hum, it may be a failing capacitor or a defective relay coil inside the unit. Since this is an internal component failure, the unit will need to be replaced under warranty.

Heads Up

• Warning: High-voltage electric heating systems can be lethal. Never open the thermostat faceplate while the breaker is on.
• Avoid Overtightening: While connections must be firm, overtightening the terminal screws can strip the threads or shear the copper wire, which creates a permanent fire hazard.
• Wire Integrity: If you see any melted plastic or blackened copper during your inspection, do not simply tighten the screw. Cut the damaged section of the wire, strip it fresh, and re-terminate the connection.
• Annual Check: Thermal expansion and contraction (heating and cooling cycles) can naturally loosen screws over time. It is a good practice to check terminal tightness every two years.