You need to set the R-switch and use both terminals. This is a common setup.
- On the T9 wall plate, locate the R-switch. It's a small plastic slider near the R and Rc terminals.
- Set the R-switch to the DOWN position. This configures it for two R wires.
- Insert your Rc wire into the Rc-terminal.
- Insert your Rh (or R) wire into the R-terminal.
- Push down on the terminal tabs to seat the wires fully in the inner holes. Gently tug to confirm they're secure.
If that didn't work: Double-check your wiring photo from the old thermostat. If you had a single R wire (or a jumper between Rc and Rh), the R-switch must be in the UP position and that single wire goes into the R-terminal. Using the wrong switch position will cause a power fault.
Heads up: Always turn off power at the breaker before handling wires. Label every wire from your old thermostat before disconnecting anything.