Don't worry, this usually has a simple fix. The most common cause after an installation is a safety switch being triggered.
- Check the furnace door. Go to your furnace. Ensure the access panel or door is completely closed and latched. Many furnaces have a door switch that cuts all power if the panel isn't securely fastened. Open and firmly re-close it.
- Verify the power switch. On the side of your furnace or air handler, there's often a standard light switch that acts as a local power cutoff. Make sure it's in the ON position.
- Re-check the breaker. Go back to your circuit breaker box. The breaker for the HVAC system might look like it's on but could be in a tripped middle position. Flip it fully OFF, then back to ON.
If that didn't work, the issue is likely at the thermostat wiring or the furnace control board. Go to the furnace and locate the control board. Ensure the thermostat wire bundle is connected securely, especially the C and R wires. A loose wire here means no power signal gets back to the thermostat.
If you're not comfortable working inside the furnace, this is the point to call a technician. There could be a blown fuse on the control board.