How the washing machine door lock system works (by Capitan Farloc)

Indice

Have you ever tried to open the washing machine door while it was running? If you have, you’ll know it just won’t budge! That’s thanks to a clever safety feature called the door lock system (or door interlock), which prevents the door from opening during operation. In this guide, we’ll explain how this system works, why it’s important, and what can go wrong with it.

What is the door lock or "electro-lock" on a washing machine door?

For many years now, washing machines have been required to include a safety device that fulfills two very important tasks to prevent anyone (especially children) from coming into contact with the drum while it’s in motion:

It blocks the washing machine’s functions from starting if the door isn’t properly closed.
It prevents the door from opening for the entire time the washing machine is operating.

The washing machine door lock is important for the safety of children in particular.

Door lock is the casual name often given to what is technically called the "electro-lock" or "closure sensor/actuator." Of course, there are many types across different washing machine brands, and even different models from the same brand often have electro-locks designed in various ways. But even though they might have different names and shapes, most of them work based on the same principle.

Examples of different models of electric locks or door locks

Where is the electro-lock located?

It’s usually positioned at the opening (1) of the washing machine where the "latch" (2) from the door fits in. To remove it, there are three options, and the best choice depends on the specific washing machine model you’re repairing:

From the top: By taking off the washing machine’s top panel, you can see the electro-lock mechanism. Tilting the washing machine backward causes the drum to shift away from the front panel, allowing access to remove the mechanism.
From the door: By removing the rubber seal between the door and the drum, you can reach and remove the electro-lock.
From the bottom: By tilting the washing machine backward, the drum moves away from the front panel, making it possible to reach and remove the mechanism.

Where is the electric lock located?

What are its functions?

Most washing machine door locks are electromechanical and don’t contain any electronic components inside. The lock has three “Faston” connectors—two for power supply and a third one that provides the “go-ahead” signal for the washing machine to start, provided that all conditions are met. Specifically, the conditions are:

The machine is powered (plugged in, switched on, and a washing program is selected).
The door is properly closed.
The door locking system has been activated, so the door can’t be reopened.

When the door lock detects that all three conditions are met, it closes an electrical contact, sending power to the third wire, which is used to supply nearly all of the washing machine’s electrical components.
Warning: If the electro-lock doesn’t work properly, almost all of the washing machine’s functions will fail, meaning it won’t load water, spin the drum, heat, etc.

The electric lock is designed to prevent the door from being opened when the washing machine is in operation.

How does it work?

The mechanism that holds the "latch" (that’s the name for the little tooth on the door) has a movable part. Once the door is closed, this part is shifted, allowing it to do two things "mechanically": detect that the door is closed and lock it in place, preventing it from reopening by blocking its movement in the new position.

Seat of the latch of an electric lock

Inside, it essentially functions as a switch connecting terminals 1 and 3. The mechanical shift of the switch from the “open” position (its resting state) to the “closed” position happens via the deformation of a "thermocouple" or "bimetallic strip." This strip has a unique property—it bends when heated and returns to its original shape as it cools. The bimetallic strip is heated by an element connected to terminals 1 and 2.
The plastic latch highlighted in the photo with a red circle is pulled up during the movement that closes the electrical contact and serves two key purposes:

It prevents the electrical contact from closing unless the mechanical part shown in the previous photo is moved, meaning the door isn’t properly closed.
It locks the mechanical part from the previous photo in place once it has moved, ensuring that the door cannot reopen.

How the electric lock works

Operational summary diagram

The electrical scheme of this mechanism is pretty straightforward and can be outlined as follows:

Contact (1) is the common wire shared by both the heating element and the switch.
Contact (2) is the second connection point for the heating element.
Contact (3) is the second connection point for the switch.

When measuring the resistance between the connectors of the heating element with a tester, it should range between 1000 and 6000 OHMS.

Electrical diagram of the operation of an electric lock

In this photo, you can see the disassembled parts of the switch, particularly the strip with the electrical contact, the bimetallic strip or thermocouple, and inside the door lock, the heating element.

View of the elements that make up the washing machine's electric lock

Testing and repairing the electro-lock

The first test to check if the electro-lock is working is simple: turn on the washing machine, wait a few seconds, and try opening the door. If it opens, then there’s likely an issue with the electro-lock. Another straightforward test is to measure the resistance of the heating element connectors using a tester. If the resistance is infinite (interrupted), the electro-lock definitely needs replacing. Unusual blackening on the electrical contacts of the switch inside the electro-lock can also indicate a problem.
Although a burnt heating element is the most common reason for an electro-lock malfunction, there could be other causes, like mechanical damage or deformation, which can only be checked visually. It’s worth noting that, because the heating element is inside, some blackening both inside and outside the electro-lock casing is fairly normal, so this alone isn’t a definitive sign of malfunction.
To repair it, you can clean the switch contacts and those on the heating element using an electrical contact cleaner spray and lubricate moving parts with silicone grease designed for plastic.

A visual check must be done on the electric lock to verify its functioning.

If you have any questions, suggestions, or just want to let us know if you liked the article, feel free to join the discussion in the dedicated thread on the forum:
<Come Funziona una Lavatrice - FORUM> (unfortunately the forum is only in Italian, but we try to answer also to messages written in English).
If, on the other hand, you’re curious about the overall functioning of a washing machine, you can check out this article. It explains (or at least I hope it does) all the stages of a washing process step by step from the perspective of the components that make it happen.
How a washing machine works (by Capitan Farloc)

Thank you
Luciano (Capitan Farloc)

Warning!

The advice and instructions provided on this site come from hobbyists rather than professional technicians, meaning there is no guarantee that they are accurate or represent the best solution.
Additionally, using the tools and techniques described here should be done with careful consideration of one’s own abilities.
These articles assume that the tasks will be performed by individuals with the necessary skills and knowledge to use the required tools safely, without risking harm to themselves, others, or property.
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Before undertaking any DIY activity, it is strongly recommended to read the Safety Notice, which provide a basic (though non-exhaustive) list of precautions to follow.

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