Inducer fan assembly or inducer control circuit board failing
Generally speaking, a motor either works or it doesn't.
Intermittent problems are usually either the controlling device, in this case the relay on the board, or wire splices/connectors.
Here's how I would go about troubleshooting this; first, get the system to call for the inducer fan to run. Next, check for voltage across the motor leads. Most likely 120AC, but could be 24AC. If there's voltage across the motor, but it doesn't run, then the motor is bad.
If no voltage across the motor, look for voltage across the relay contacts. If there's voltage across the relay contacts, then it's not conducting. Look for voltage across the relay coil. If you have coil voltage (usually 24AC), and voltage across the contacts, then the relay is bad.
Look for voltage across fuses. If you have voltage across a fuse, it's blown.
These are basic tests, there are alot more if needed.