My Mysa is showing H2. What do I do?

Danger: The installation of high voltage equipment should be performed by a qualified electrician. Please ensure that you comply with local electrical codes and regulations. Improper installation can lead to device failure and even cause a fire. Damage to thermostat due to improper installation is not covered under warranty.


The H2 error is a result of an incomplete (open) heating circuit. To complete the heater circuit:

  • Mysa’s LOAD connection must make contact with the heater supply connection; and
  • Mysa’s L2 (N) wire must make contact with the heater return wire.

The other scenario is that the heater return wire in the L2 or Neutral bundle is not making contact with the other wires in the wire nut. This is more prone to happen as you increase the number of wires in the wire nut.

If you need help determining your specific wiring configuration, consult this guide

If you're sure the thermostat is correctly wired, it's possible there's a poor connection between Mysa's load wire and the heater's wire in the wire nut itself. If this is the case, remove Mysa, and make the wire nut connection again. Follow this guide to learn how to correctly use a wire nut.

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