Motor will not start up (or hums)
There are two types of motors used. The shaded-pole motor and the split-phase motor. If you have a split-phase motor it has a relay, like the picture below. The solid-state relay was used to allow the energizing of the start winding. This would allow the motor to achieve approx 80% of the rated speed. Then the relay would de-energize the start winding to prevent overheating. There is no attachment between the motor and the relay, except for the wiring.
This is what a starter relay looks like. If your heater has one, check to see if it is energizing the starter windings at start-up. If not it is probably defective. You can find one at EquipSupply.com.
If your motor does not have the relay, then the motor has an internal start-up system. Those are shaded-pole motors. Unfortunately, they are not serviceable, but you can replace the motor. Here’s an example of a shaded-pole motor. These can also be found at EquipSupply.com.
The motor usually has the part number printed on it. However, the number on the label may not be the current part number. Please refer to our heater reference charts to find the correct motor and correct relay, if applicable. Use your heater’s model number.