Quick Answer:
A loud snap or bang when the washer stops filling is usually water hammer: a valve (the washer’s solenoid) closes quickly and sends a pressure shock through the pipework. Run a fill cycle while watching and feeling the hoses and valves to confirm whether the noise lines up with the solenoid closing. If the laundry box is recessed or access is tight, a plumber can add proper arrestors to stop the shock and protect joints from developing leaks.
Why This Happens
When the washer finishes the fill stage the solenoid valve shuts off the water suddenly. That abrupt stop causes the moving column of water to slam against a closed valve or a change of direction in the piping, creating a sharp bang. The problem can be worse if there’s no cushioning device (hammer arrestor) near the valve or if the piping is long, rigid, or poorly supported.
This is the same physical shock homeowners notice with other fixtures, as in Pipes bang when ice maker shuts off and after changes to control hardware, like a Hammer after installing smart shutoff valve.
Step-by-Step What to Do
1. Prepare for an easy test
- Make sure the washer is on a normal fill setting and empty of clothes.
- Keep the access to the laundry box clear so you can look and reach behind the machine if needed.
2. Run a fill cycle and watch
- Start a fill cycle and watch the washer as it takes water. Note when the water stops and the machine changes stage.
- Pay attention for the bang — does it occur exactly when the water flow stops? That timing points to the solenoid closing as the cause.
3. Feel each hose at the shutoff to identify hot vs cold
- With the machine filling, carefully feel each supply hose near the shutoff valve (not the electrical components). One will feel warm or hot, the other cool — this tells you which valve controls which temperature.
- Knowing which line bangs helps isolate whether the issue is on the hot or cold side.
4. Check for hammer arrestors at the laundry box
- Open the laundry box cover and look for small cylinder-shaped arrestors, short stub pipes, or back-to-back fittings close to the valves. These reduce sudden pressure spikes.
- If you don’t see an arrestor, the line may rely on a different device or have none at all.
5. Repeat the test on the opposite temperature
- Run another fill cycle selecting the other temperature (hot if you first tested cold, or vice versa) and see whether the bang follows that side instead.
- Document which side produces the noise; it helps a plumber target the fix if needed.
6. If the laundry box is recessed or access is tight
- A recessed box or cramped access can make installing proper arrestors difficult. In those cases a plumber can add purpose-built arrestors or reposition piping without damaging the wall or boxes.
What Not to Do
- Don’t kink hoses or overtighten hose washers to “slow the water.” That can damage hoses, cause leaks, or create extra pressure issues.
- Don’t pull the washer box loose from inside the wall if it’s installed there and you’re not comfortable with that work. If the washer box or valves are inside the wall and you’re not comfortable accessing them, call a plumber instead of pulling the box loose.
- Don’t ignore a repeating loud bang—continued shocks can loosen fittings and eventually cause leaks.
When to Call a Professional
- If the bang continues after you confirm timing and there’s no arrestor at the laundry box, call a plumber to install a proper hammer arrestor or pressure-absorbing device.
- Call a plumber if the laundry box is recessed, hard to reach, or part of a wall cavity you’d rather not disturb—professionals can fit arrestors without damaging finishes.
- Also call a plumber if you find loose fittings, active leaks, or any corrosion at the valves that suggest a joint might fail.
Safety Notes
- Turn the washer off and unplug it before moving the machine to access the laundry box to avoid electrical hazards.
- Turn off the supply valves before touching hoses or fittings. Open the valves slowly when testing to avoid sudden pressure changes.
- If you are unsure about working behind the washer, have limited space, or the valves are inside the wall, call a professional rather than forcing access.
Common Homeowner Questions
- Why does it only happen sometimes? Short answer: timing and pressure. If the washer’s valve closes faster at certain cycles or water pressure varies, you’ll hear it intermittently.
- Will adding arrestors stop leaks? Short answer: Arrestors reduce shocks that loosen fittings, so they lower the chance of leaks but won’t fix an already leaking joint.
- Can I install arrestors myself? Short answer: Possibly, if the laundry box is accessible and you’re comfortable turning off water and tightening fittings; otherwise hire a plumber.
For more related articles, see the Pipes Banging After Fixtures Turn Off hub.