Gen3: Error codes

Last updated: November 4, 2026

Gen3 can show H1, H2, H4, and H5. Some of these share a name with codes on V1, V2, or Lite, but Gen3 detects them by measuring the current flowing to your heater, so use this page for Gen3 (model MYSA BB V3-0). H4 means the same thing as on V2 and is always a safety problem.

This is line-voltage equipment. If you need to inspect wiring, turn the breaker off first and confirm power is off. Do not work live.

H1: Over-temperature

The thermostat's internal temperature went above its safe limit, so it stopped heating.

What to do:

  1. Turn the breaker off.

  2. Make sure the heater is not blocked and the thermostat is not sitting on another heat source.

  3. Restore power only after the area has cooled.

  4. If H1 returns, leave the breaker off and contact Mysa Support.

H2: Heater not drawing current

Gen3 shows H2 when it turns the heat on but measures almost no current flowing to the heater. Most often, the heater wire isn't connected to Mysa's Load wire, or a wire nut is loose. It can also appear if the heater is connected but isn't drawing power for another reason.

What to do:

  1. Turn the breaker off and confirm power is off.

  2. Find the wire that goes to the heater. On your old thermostat it was on the terminal marked Load (or T1), or it has a "Load" tag. Mysa's Load wire must be joined to that wire, whatever colour it is.

  3. Reversed colours: if the red (or white) wires were on your old thermostat and the black wires were capped together in the box, wire by function, not colour. Mysa's L1 and Load wires go to the red wires that were on the old thermostat (L1 to the supply, Load to the heater wire). Mysa's L2/N wire goes to the bundle of black wires that were capped together. Mysa's wire colours will not match your house wires.

  4. Make sure Mysa's Load wire was not cut short or left capped off on its own. It must be connected.

  5. Check every wire nut and give each wire a gentle tug. Connections can loosen when there are several wires in one nut.

  6. Turn the breaker back on and raise the setpoint to call for heat. If H2 comes back, leave the breaker off and contact Mysa Support with a photo of your wiring.

If you are not comfortable working on line-voltage wiring, leave the breaker off and contact Mysa Support or a licensed electrician.

H4: Current while output should be off

The thermostat measured current through the heater when output should have been off. This means power can reach the heater even when Mysa is not calling for heat, so the heater may keep running. This is the same condition as H4 on V2. Treat it as a safety problem.

What to do:

  1. Turn the breaker off now and leave it off. Do not keep using the thermostat while H4 is showing.

  2. Do not turn the breaker back on to test or clear the code, and do not try to clear it from the app. If H4 goes away on its own, still leave the breaker off.

  3. Contact Mysa Support and tell them you have a Gen3 (MYSA BB V3-0) showing H4. Send a photo of the display.

H5: Over-current

H5 means over-current. It appears when the measured current goes above approximately 18 A. Gen3 is rated for a maximum of 16.7 A.

On V2, H5 is a different relay check. Gen3 uses a triac, not a relay, so that check doesn't apply. There is no H6 on Gen3.

The circuit breaker rating alone does not confirm heater compatibility. Keep the combined heater load within 4,000 W at 240 V or 2,000 W at 120 V.

What to do:

  1. Turn the breaker off.

  2. Add up every heater on that circuit. If the total is above 4,000 W at 240 V or 2,000 W at 120 V, reduce the load before restoring power.

  3. Do not restore power until the load is confirmed safe.

  4. Contact Mysa Support or a licensed electrician. Tell them this is Gen3 (MYSA BB V3-0) and you saw H5.

How Gen3 codes differ from V1, V2, and Lite

  • H2: the fix is similar on every model (check the connection between Mysa Load and the heater). On Gen3, H2 is triggered by low measured current while heating.

  • H4: same meaning as V2 H4: power reaching the heater when it should be off. Breaker off, leave it off, contact support.

  • H5 and H6: V2 H5 and H6 (relay checks) do not apply here. On Gen3, H5 is over-current only, and there is no H6.

  • A blank display, a pairing problem, or no heat without a code is not an H-code. Use the pairing or power articles for those.

When you contact support

Include:

  • A photo of the display showing the code

  • A photo of your wiring (for H2 or H4)

  • Model: Gen3 (MYSA BB V3-0)

  • Voltage (120 V or 240 V) and heater wattage if you have it

  • What the heater was doing when the code appeared

Email: support@getmysa.com (general) or install@getmysa.com (wiring).