Short answer: A single loud bang right when water shuts off quickly (washing machine, dishwasher, ice maker, a lever faucet) is water hammer: the moving water stops suddenly and the shock travels through the pipes. Common fixes are water hammer arrestors near the appliance valves, securing loose pipes and lowering excessive water pressure.
Quick diagnosis
| What you notice | Most likely cause | What to check | Call a pro? |
|---|---|---|---|
| Bang when the washer or dishwasher valve closes | Water hammer from fast-closing solenoid valves | Notice if the bang matches the valve | Often for arrestor install |
| Bang when you shut a faucet quickly | Water hammer | Close the faucet slowly and compare | Sometimes |
| Rattling as water runs | Loose pipes against framing | Look for unsecured pipes in the basement | Sometimes |
| Banging from the water heater | Sediment in the tank | Listen at the tank while heating | See water heater guides |
| Noise everywhere and high pressure | Pressure too high or failing PRV | Test pressure with a gauge | Often |
What water hammer is
When a valve closes suddenly, the moving water stops and creates a pressure surge that can make pipes bang. This Old House describes a water hammer arrestor, a small cushioned chamber installed near the valve, as the standard fix. Manufacturers such as Watts make arrestors for washing machine boxes and fixture supplies.
How to reduce it
- Install water hammer arrestors at the washing machine and dishwasher supplies.
- Secure loose pipes with straps so they cannot slap against joists.
- Check the house water pressure; very high pressure makes hammer worse, and a pressure-reducing valve may need adjusting.
- Older homes may have air chambers that have filled with water; draining the system can restore them temporarily.
When to call a professional
- The noise is violent or started suddenly.
- You see leaks at fittings.
- Water pressure is very high or the PRV needs service.
- Arrestors need to be added inside walls.
What it usually costs
Screw-on arrestors for a washing machine cost a modest amount at hardware stores. Installing arrestors in walls or adjusting a PRV is plumber work at $45 to $150 per hour (HomeGuide, 2026).
Frequently asked questions
Is water hammer dangerous?
Repeated pressure spikes can loosen fittings and damage valves and appliances over time, so it is worth fixing.
Why do my pipes bang when the toilet fills?
A fill valve that shuts off quickly can cause hammer, especially with high water pressure.
Related problems
Sources
- This Old House: How to quiet pipes with a water hammer arrestor
- InspectAPedia: Water hammer pipe banging noise FAQs
- HomeGuide: Plumber cost per hour (2026)
This guide is general information, not a substitute for an inspection by a licensed professional. See our disclaimer.