Installation & Wiring Troubleshooting — Mysa for In-Floor Heating

Last updated: September 2, 2026

Ran into a problem while installing Mysa for In-Floor Heating? Work through the symptom that matches what you're seeing.

Warning Mysa for In-Floor Heating connects to high-voltage (single-phase 120/208/240 VAC) wiring. Turn off the breaker and verify with a non-contact voltage tester before touching any wires. If you are unsure, consult a qualified electrician.

Quick error code reference

Code

Meaning

Typical cause

H2

Open heating circuit

No heater load detected

H3

GFCI trip

Ground fault detected

I3

Floor sensor issue

Sensor loose, disconnected, or out of range

Thermostat won't power on after installation

  1. Turn off power at the breaker immediately.

  2. Recheck every connection against the wiring diagram for your voltage — line to the line terminals, load to the load terminals.

  3. Confirm no bare wire is exposed outside the wire nuts and that no wires were pinched when folding them into the gang box.

  4. Restore power and test again.

H2 — Open heating circuit

The thermostat detects no heater load on the circuit.

Possible causes:

  • Heating mat not connected

  • Loose wire connection

  • Damaged heating element

How to fix:

  1. Turn off power at the breaker

  2. Check that the heating mat wires are securely connected to the LOAD terminals

  3. Verify the heating mat is not damaged

  4. Restore power and test

Warning Turn off power at the breaker before checking any wiring connections.

H3 — GFCI trip or FAULT light on

The built-in GFCI detected a ground fault and tripped for safety.

Possible causes:

  • Ground fault in the heating mat

  • Moisture in the electrical connections

  • Damaged wiring

  • Mysa installed on a circuit that already has GFCI protection

How to fix:

  1. Press the RESET button on the thermostat

  2. If it trips again immediately, there may be a ground fault in the system

  3. Check for moisture or damage in connections

  4. Confirm the circuit is not already GFCI-protected — a GFCI breaker or GFCI outlet upstream will conflict with Mysa's built-in GFCI and cause constant nuisance trips. Have an electrician fit a standard (non-GFCI) breaker.

  5. Contact an electrician if the issue persists

Caution Repeated GFCI trips indicate a potential electrical fault. Do not bypass the GFCI. Have the system inspected by a qualified electrician.

If the FAULT light stays on indefinitely right after installation, the GFCI can no longer safely detect current. Contact support.

I3 — Floor sensor issue

The floor sensor is not reading correctly.

Possible causes:

  • Sensor wire disconnected

  • Sensor damaged or broken

  • Sensor resistance outside the 5K–40K Ohm range

How to fix:

  1. Turn off power at the breaker

  2. Check that the floor sensor wires are connected to the sensor terminals

  3. Verify the sensor wire is not damaged

  4. If using an existing sensor, confirm it's within the 5K–40K Ohm range

  5. Recalibrate the sensor in app settings if needed

Tip If you installed a backup sensor during initial setup, you can switch to it without needing to access the floor.

Still stuck?

For the full error code reference, see Error Codes — Mysa for In-Floor Heating.

If your wiring doesn't match these descriptions, or you're unsure about any connection, contact our team with a photo of your wiring.

Installation questions: install@getmysa.com