How a washing machine's solenoid valve works (by Capitan Farloc)

Ever wondered how your washing machine knows exactly when to let water in? That’s all thanks to the water inlet valve, also known as the solenoid valve. In this guide, we’ll explain how it works, where to find it, and what might cause it to fail. A handy read for DIYers and anyone curious about how washing machines work!

What is a solenoid valve?

A solenoid valve is basically a faucet (...valve) controlled electrically (solenoid...) that allows fluid to pass through. In a washing machine, the solenoid valve is used to let water in to fill the drum for washing. It’s usually located at the back of the washing machine, right where the threaded connection is—where you screw in the water supply hose. In fact, most of the time, the threaded connection is already part of the solenoid valve itself.

What does it look like?

From the inside of the washing machine, the solenoid valve looks roughly cylindrical, with a cone-shaped end where the connection for the hose leading water to the detergent drawer sticks out.
You can also spot the threaded rear part (the one for screwing in the water supply hose, as seen in the previous photo), which is positioned towards the outside of the washing machine.
The whole structure is topped with a solenoid, from which two electrical contacts stick out. These are used to control the valve's opening.

How is the solenoid valve controlled to load the right amount of water?

In a washing machine, water needs to be filled up to an optimal level set at the factory—one level for washing, and usually a different one for rinsing.
The solenoid valve is used to let water into the machine, but how does it know when to stop? That’s where the "pressure switch" comes in. It detects when the desired water level is reached and cuts off the power to the solenoid valve accordingly.
The simplified diagram next to this explanation is just to show the basic working principle, but of course, the electrical connections are much more complex and are managed by the Washing Programs control unit.

The water loading system inside the washing machine

If you take a look inside the washing machine by opening the top panel, you'll see the components mentioned earlier. At the top left of the photo, you'll find the solenoid valve (A) with electrical wires attached to activate it. From the solenoid valve, a connecting hose (B) runs to the detergent drawer (C) to bring the water in. Underneath the detergent drawer is a rubber tube (not visible in the photo) that directs the water into the washing drum. Finally, the hose (D), which goes from the washing drum back to the detergent drawer, serves as an air vent.

Detailed operation of the solenoid valve

When the solenoid valve isn’t powered, it has a “self-closing” system that’s independent of the water pressure in the hydraulic circuit, and it works like this:
Water enters through duct (A) and pushes against the surface (B) of the membrane (C). As water moves through duct (D), it also reaches the upper part, pressing against the surface (E) of the membrane. Even though the pressure above and below the membrane is the same, the surface area that water “presses” on at the top is much larger than the corresponding surface area at the bottom. As a result, the force pushing the membrane downward is greater than the force pushing it upward, so the membrane stays pressed against the lower duct and the “valve” remains closed.

When the electromagnet (F) is powered, the armature (G) is attracted and lifted, freeing the hole in the center of the membrane (C). This allows the water in chamber (E) to flow out. This causes an immediate drop in water pressure on the upper part of the membrane (E).
At this point, the situation flips: the force pressing the membrane downward becomes weaker than the force pushing it upward. As a result, the membrane lifts, opening duct (H) and allowing water to pass through. This means the "valve" is now open.

Faults, symptoms, and solutions

If the solenoid valve doesn’t work properly or only partially functions, it usually results in the drum not filling properly, which generally causes the washing machine to stop working.
Let’s take a look at some of the most common issues and the related tips for fixing them.

Reduced water flow

When water loading happens very slowly, you can open the detergent drawer and see the water coming out in a weak stream. Sometimes, the washing machine might even show an error before starting the wash cycle, indicating there could be a problem with reduced water flow. One of the most common causes of this issue is a clogged filter at the connection point of the water supply hose, often due to accumulated rust or limescale residues.
Cleaning the filter is quite simple—just grab it gently with long-nose pliers and carefully pull it out of its housing. Once removed, you can clean it under a stream of tap water or, in more “stubborn” cases, soak it for a few hours in a limescale remover or, even better, ordinary kitchen vinegar.

Electromagnet malfunction

If the water doesn’t load at all, the detergent stays in the drawer, and after a while, the washing machine shows an error, it could be due to a malfunction of the electromagnet that triggers the solenoid valve to open. This issue is usually caused by a broken copper winding that forms the solenoid (or electromagnet), which is responsible for opening the valve.
 To check if the winding is intact, you’ll need a multimeter (or tester) set to measure resistance in the 20K (20 KiloOhm) position. By placing the probes on the two connectors of the solenoid valve, you should measure a resistance of about 3 or 4 KOhm (3,000–4,000 Ohm). If the winding is broken, the resistance will be infinite, and this condition is usually indicated on digital testers by a lit “1” on the left side of the display. In this case, the only solution is to replace the entire solenoid valve with either an original or compatible spare part for your washing machine.

Internal mechanism blockage

If the check from the previous step was successful but the solenoid valve still doesn’t work, we could be dealing with a mechanical blockage. A simple way to check if the solenoid valve is working or stuck is to power it directly. To do this, follow these steps:

1. First, unplug the washing machine and disconnect the Faston connectors from the solenoid valve.
2. Then, after confirming from the valve’s specifications that it requires 220V AC power, create an electrical cable with a plug and insulated Faston connectors.
3. With the water hoses connected (both inlet and outlet), attach the insulated Faston connectors to the appropriate terminals on the solenoid valve.
4. Keeping a safe distance, plug the cable in. If the solenoid valve is functioning, you should hear the sound of water flowing through the hose into the detergent drawer and drum.

If powering the solenoid valve this way doesn’t open it, it’s definitely stuck and will need to be replaced. However, if the solenoid valve works, the issue is further upstream and could be caused by various problems, such as:

• A malfunctioning door lock mechanism.
• A break in the wire powering the solenoid valve.
• A fault in the washing machine’s program control unit.

I hope this article was helpful and interesting!

If you have any questions, suggestions, or simply want to let us know whether you liked the article, you can 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 workings of a washing machine, feel free to check out this article. It explains (or at least I hope it does) the entire washing process step by step from the perspective of the components that make it all happen.
How a washing machine works (by Capitan Farloc)

Thank you
Luciano (Capitan Farloc)