I replaced the big fan motor an capacitor and it just hums when I turn switch to on . I can hot wire it and it runs fine. I want to check the little cobustion fan but it has four wires two for power and two for a sensor on the ventilation fan?

If you connect the 2 wires that go to the sensor, Fan will run all the time, instead of turning off when heat is present.

So why does the ventilation fan hum but when I hot wire it it runs great? Oh thanks for your answer. I assumed that but didn't want to screw something up on those four wires!