Warning! High Voltage!!
Any work with high voltage equipment can be dangerous or even fatal if you do not take proper precautions. You should never work with live wires. 

The H2 error is a result of an open heating circuit, resulting in Mysa not detecting a heater load.

What does this mean?
It means that, in most cases, wires connecting your Mysa to your heater are either loose or incorrectly connected.

Here’s how Mysa works! 

Electricity flows into your Mysa, Mysa receives and regulates the electrical load and sends commands to your heater to turn ON or OFF. If successful and the commands reach the heater, the electricity is then converted to heat.

The H2 error code on your Mysa’s display means that your Mysa is receiving power from your home’s wiring - it wouldn’t turn on if it didn’t! In this case, Mysa tries to send a command to the heater, but the heater circuit gives no response. In electrical terms, this means Mysa is not detecting a heater load. This is likely due to an issue with wiring between Mysa and your heater.


Heater Circuit Troubleshooting

Did you follow our Installation and Compatibility Guide

If you did, here’s a quick refresher:  

L1 = Power supply from breaker

L2 = Neutral (120V) / Second phase leg (240V)

Load = Heater Load


To complete the heater circuit:

  • Please make sure Mysa’s load connection is making contact with the heater supply connection.
  • Mysa’s L2 (N) wire is making contact with the heater return wire.


Here are the three most common wiring scenarios: 

1) 240v, 4 wires, 1 heater V1240V_4_wires.png

2) 240v, 6 wires, 1 heater V1240V_6_wires_1_heater.png

3) 240v, 6 wires, 2 heater V1240_6_wire_2_heaters.png


Another possibility  is that the heater’s return wire in the L2 or neutral bundles is not making secure contact with the other wires in the wire nut. If you need help determining your specific wiring configuration, check the guide.

Loose Wire Connection Troubleshooting
Everything looks fine, the wires are all matched properly. What’s next?

Your wiring connection may simply be loose! Ensure that your breaker is OFF  and go back to your Mysa’s wiring. Here are some common issues we see:

  • The wire nuts are not applied correctly. Wire Nuts aren’t just a “cap” for the wires! They’re a tool to make sure the wires twist together securely for a secure connection. Make sure that you are using them to perform the actual connection and not just placing them on top; wire nuts must be tight and secure without leaving exposed wire. 
  • You disrupted the connection when placing your Mysa back into the gangbox. Before you secure your Mysa to the wall and turn your  breaker ON, make sure you carefully place the wired connections back in the gangbox. Hastily or forcefully pushing them in  may cause an otherwise ideal wiring connection to become loose. This could happen immediately or gradually if H2 displays after your Mysa has been functioning properly for a period of time.  
  • There’s too much (or too little) exposed wire. Is one of your wires mostly exposed copper? Or is the exposed part of the wire much shorter than expected? Make sure that the length of exposed wire is similar in length to the exposed wire that comes with the Mysa. Use a wire stripping tool if necessary. When applying the Wire Nuts, make sure there isn’t any bare wire exposed.TooMuch-Or2Little-Wire.gif


Other Troubleshooting Suggestions

Still having issues? Consider the following:

  • Your Home’s Wiring

Did you make any changes to your home’s electrical wiring system, or is this part of a new home installation?
If yes, try swapping the L1 and the Load as shown in the diagram, or consult with a certified electrician if you are not confident that the heater itself is wired correctly. 


Warning! High Voltage!!
Any work with high voltage equipment can be dangerous or even fatal if you do not take proper precautions. You should never work with live wires. 


  • A Problem With Your Heater

Did you buy Mysa to replace a thermostat that stopped working?
If yes, it may have actually been the heater that malfunctioned - not the original thermostat.

Is it a commonly used heater in your home? Are you confident it was working before you installed your Mysa?
If the answer is no, you may want to check with an electrician that the heater is actually still functional. While electric heaters usually have a long lifespan, they can fail.

  • Electrical Specifications

Did you correctly check Mysa’s electrical specifications before installing your Mysa?
Mysa’s electrical requirements are very specific but should cover the vast majority of residential electric heating installations. While Mysa devices are safety certified, we do not recommend you exceed an amperage of 16A or a wattage of 3800W. Doing so may cause the H2 error to appear, although it is uncommon. 


High five! We hope this article helped you resolve your H2 error code. 

Still having issues? Reach out to our all-human Customer Experience team!

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