It can be quite simple to repair an electric heater, as long as you can get replacement parts for it from the manufacturer. In many cases, it is not a replacement part that's needed, but simply some standard maintenance. With the passing of time, any number of things can happen to our electrical devices, and the most common problem is dust building up inside the unit.
This dust can cause all kinds of issues, such as seeing smoke or smelling strange odors. In the case where your unit won't turn off, you are looking at one of two things causing the issue: either the power switch is shot or the temperature sensor is broken.
Step 1 - Open the Case
In some cases, your actual casing on the heater may be held together with special screws or bolts, such as stars or hex bolts. You will need specialized tips and a socket tool to get inside to repair your electric heater. The reason behind this is to prevent children from taking them apart easily and causing burns or electrical shock.
You will, of course, want to make sure the unit is not plugged into the wall while you are opening the case for the same reasons. Once you have the case opened, you are going to see the important parts that make your device run: your power switch, heat or temperature coil, and the heater elements. In some models that are a little more advanced, there may even be a circuit board, and the coils might be wrapped around ceramic cylinders.
Step 2 - Check Voltages
Once the case is open, you are going to check for burnt out circuits or switches in the unit by using your voltage meter to check for moving or dead current. You can identify the part you will need to repair in the electric heater by doing this. Again, be careful as not to touch the coils in the unit to avoid burning or searing your skin.
The voltage meter is only going to work to check the electrical current on the positive and negative poles of the power switch and the circuit board. In some models, these parts can be ordered directly from the manufacturer, and the parts have a replacement number attached to them based on the make and model of the unit.
Step 3 - Check the Temperature Coil
If your heater turns on and off fine, but it just does not turn off once it hits a preset degree of heat, it is likely that your temperature sensor is burnt out and will have to be replaced. To repair this part of an electric heater, you will need to order the correct part and then simply take the old one out of the unit and replace it.
They generally are screwed into place on the inside of the unit away from the heater coils and can easily be removed and replaced. Again, check with the unit's manufacturer to see what parts can be ordered and replaced.