my new mysa thermostat says 'no power' on the screen and my baseboard heaters are cold, did i wire it wrong?

Diagnosis

The "No Power" message on a Mysa Smart Thermostat indicates that the device's internal power circuitry is not receiving the necessary 120V or 240V input from the electrical panel. Unlike low-voltage thermostats that rely on a C-wire from a furnace, the Mysa is a line-voltage device that draws power directly from the heating circuit. If the screen is blank or displaying this error, the circuit is open, meaning electricity is not reaching the thermostat's logic board. This most commonly occurs due to a "Line/Load" reversal. In a standard baseboard setup, the "Line" wire brings power from the breaker, and the "Load" wire carries power to the heater. If these are swapped, the thermostat may not boot up because it is trying to draw power from the heater side of the circuit rather than the source. Additionally, a loose neutral wire (typically white) will prevent the device from completing the circuit, resulting in a total power failure even if the hot wire is connected correctly. You can confirm this by using a non-contact voltage tester at the wall box; if the "Line" wire is dead while the breaker is on, you have a wiring or breaker issue.

How to Fix It

To resolve the power issue and restore heat to your baseboard radiators, follow these precise electrical steps. Ensure you are working with the correct voltage for your specific Mysa model (120V vs 240V) as they are not interchangeable.

1. Isolate Power: Go to your electrical panel and switch off the circuit breaker dedicated to the heating zone. Verify the power is off by attempting to turn on the heater or using a voltage tester on the wires.
2. Remove Faceplate: Gently pull the Mysa thermostat faceplate away from the wall base. Inspect the wiring terminals for any loose strands or "stray" copper that might be causing a short circuit.
3. Identify the Line Wire: Locate the wire coming directly from the electrical panel (the "hot" feed). This must be inserted into the terminal labeled L (Line). If you have a 240V setup, you will have two hot wires; ensure the primary feed is secure.
4. Identify the Load Wire: Locate the wire that leads directly to the baseboard heater element. This wire must be inserted into the terminal labeled 1 (Load). If these two are swapped, the thermostat will not power on.
5. Secure the Neutral: Ensure the white neutral wire is firmly clamped into the neutral terminal. A loose neutral is the leading cause of intermittent "No Power" errors. Tighten the screw terminal until the wire is immobile.
6. Verify Grounding: Ensure the bare copper or green ground wire is connected to the ground screw in the back of the electrical box to prevent chassis electrification.
7. Reassemble and Boot: Snap the faceplate back onto the base and restore power at the breaker. The device should now boot to the pairing screen.

If That Didn't Work

• Check for a Tripped GFCI: If your thermostat is on a circuit shared with a GFCI outlet (common in older renovations), check if the outlet has tripped. A tripped GFCI upstream will kill power to the Mysa regardless of how correctly it is wired.
• Test the Heater Element: Use a multimeter to check for continuity across the baseboard heater element. If the heating element is burnt out (open circuit), some Mysa models may struggle to initialize or report power errors because the load is missing.
• Inspect the Breaker: Switch the breaker completely to the "Off" position and then back to "On." Occasionally, a breaker can "half-trip," providing enough voltage to trigger a sensor but not enough amperage to boot the smart thermostat's Wi-Fi chip.
• Verify Voltage Compatibility: Confirm that you didn't install a 120V Mysa on a 240V circuit. If the voltage is too high, the internal fuse may have blown instantly upon power-up to protect the circuitry, rendering the unit dead.

Heads Up

• Avoid Over-tightening: When securing wires into the L and 1 terminals, do not over-torque the screws. Over-tightening can strip the terminal threads or shear the copper wire, creating a hidden break in the connection.
• Wire Stripping: Ensure exactly 3/8" of insulation is removed from the wires. If too much copper is exposed, you risk an arc flash; if too little is exposed, the terminal will clamp onto the plastic insulation rather than the conductor.
• Wi-Fi Interference: Once power is restored, if the device boots but cannot connect, ensure the faceplate is seated flush. A loose faceplate can occasionally interfere with the internal antenna's signal strength.
• Wait for Calibration: After a "No Power" event, the Mysa may take 5-10 minutes to calibrate the room temperature. Do not panic if the heaters don't kick in the exact second you flip the breaker.