Common Symptoms and Quick Checks

Use this chart to identify your issue and jump to the right section.

🔴 No Power / Blank Thermostat

If the Mysa for Central HVAC display doesn’t turn on after installation:

1. Check Power Source

Make sure the breaker controlling your furnace or air handler is ON.

Confirm the blower door or access panel is closed — most systems have a safety interlock that cuts power when open.

2. Inspect the Low-Voltage Fuse

Look for a 3–5A automotive-style fuse on your furnace control board.

If it’s blown, replace it with one of the same rating.

💡 If the fuse continues to blow, there may be a short circuit or incorrect wiring.
Recheck connections or consult an HVAC professional.

3. Verify RC/RH Switch Position

Mysa for Central HVAC ships with the RC↔RH switch set to Closed (to the right).

If your system uses one R-wire, the switch on the back of the display must be set to the default CLOSED position (right).

If your system uses two R-wires (Rh & Rc), switch to the OPEN position (left.)

4. Confirm C-Wire or C-Wire Adapter Connection

Mysa for Central HVAC requires continuous 24V power between R and C.
If no C-wire is available, verify the C-Wire Adapter (CWA) is properly installed.

🟠 Thermostat Powered but HVAC Not Responding

If Mysa for Central HVAC turns on but heating, cooling, or fan modes don’t work:

1. Confirm Configuration Code

Open the Mysa app → Device Settings → Thermostat Configuration
Ensure the correct configuration code is selected for your system type.
See 👉 Configuring Mysa for Central HVAC for Your HVAC System.

Wrong code can cause heating/cooling reversal or no operation.

For heat pumps, switch the last digit if modes seem reversed:

• i.e. 86P to 86L or 31N to 31L, etc.

2. Check Wiring Connections

Tug each wire gently to ensure it’s secure in its terminal.

Make sure multiple wires in one terminal (if any) are fully seated.

Confirm all terminal labels match your wiring photo or diagram.

3. Recheck Furnace Board Connections

At your furnace or air handler control board:

• Verify all wires match your thermostat’s terminals (R, C, W, Y, G).

• Ensure the C-wire is properly connected.

🔵 Device Won’t Pair

If your Mysa for Central HVAC isn’t showing up in the app during Bluetooth setup:

• Make sure your thermostat is powered and the display is on.

• Ensure your phone’s Bluetooth is turned on and within 1–2 meters (3–6 feet) of the thermostat.

• Toggle Bluetooth off/on to refresh the scan.

• Close and reopen the Mysa app.

Re-enter pairing mode on Mysa for Central HVAC by holding the top and bottom buttons together until the devcie reboots. Bluetooth icon will appear on the device when ready.

Still having trouble?
👉 Follow detailed steps in Pairing Your Mysa for Central HVAC

🟡 Configuration Mismatch or Incorrect Operation

If your system behaves incorrectly (e.g., cooling when heating is selected):

• Verify the config code in the app.

• For heat pumps, swap 31P ↔ 31L if heating/cooling is reversed.

• Recheck wiring against your original photo.

• Confirm the O/B reversing valve wire is connected to the correct terminal.

If issues persist, review the configuration match

🟢 C-wire Adapter Specific Checks

If you’re using the Mysa C-Wire Adapter, verify the following:

1. Power Indicator LED

The CWA module has a green LED that indicates 24V power presence.
If it’s not lit:

• Check that the furnace breaker is on.

• Verify the connections are secure.

2. Connections

Confirm wires from the CWA harness are connected as follows:

• Red → R

• Blue → C

• White → W (or W/O/B)

• Yellow → Y (if used)

3. Placement and Distance

The CWA should be installed close to the furnace control board — typically within 12 inches.
Avoid routing near high-voltage lines or fan relays to prevent interference.

When to Call a Pro or Contact Mysa Support

If you’ve completed the above checks and your Mysa for Central HVAC still isn’t functioning correctly, contact Mysa Support or a licensed HVAC professional.

Call a Pro If:

• Your system has two transformers (heating and cooling power supplies).

• You have a communicating or proprietary thermostat system (e.g., non-standard terminals).

• Wires are unlabeled, missing, or ambiguous (B vs C confusion).

• You’re using zone valves or complex multi-zone control boards.

• The furnace fuse blows repeatedly after checking wiring.

Professionals can verify transformer isolation, confirm 24V presence, and test control signals directly.