Diagnosis
Error 8 indicates a detected voltage mismatch or irregularity. The thermostat has measured a voltage outside its expected operating parameters.
How to Fix It
Turn off the circuit breaker. Remove the thermostat faceplate. Verify you have the correct Mysa model (V1 or V2) for your voltage system (120V, 208V, 240V). Confirm all wire connections are tight and correct: L, 1, N.
If That Didn't Work
Use a multimeter to measure the voltage between the Line and Neutral wires at the wall. It should be within 10% of your system's rated voltage (e.g., 216V-264V for a 240V system). If not, the issue is in your home's electrical supply.
Heads Up
Error 8 can also appear briefly during a power surge or brownout. If it clears after a power cycle and doesn't return, it was likely a transient grid issue.