Diagnosis
The thermostat is not detecting 24VAC power from your HVAC system's control board. This is most often due to a miswired or disconnected C (common) wire.
How to Fix It
Turn off power to your furnace at the breaker. Remove the thermostat from the wall plate. Verify you have a wire connected to the C terminal on both the wall plate and your furnace control board. The wire must be secure. Restore power.
If That Didn't Work
Check the 3A fuse on the furnace control board. If blown, replace it with an identical 3A automotive fuse.
Heads Up
If your old thermostat didn't use a C wire, you cannot use the TJ-610 without installing one or using a plug-in power adapter.