Why do my pipes bang when I shut off the water?
A sharp bang or a series of knocks when a faucet closes, a toilet finishes filling, or a washer or dishwasher valve cycles.
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Key takeaways
- This is usually not an emergency, but it does not fix itself and it gets worse if you leave it.
- Most likely cause: Waterlogged air chambers.
- Do this first: Shut off the main, open the highest and lowest faucets to drain the system, then restore water to recharge air chambers.
- Call right away if a banging pipe is followed by a visible leak or a wet ceiling.
- The repair starts with: Measure static pressure at the hose bibb.
What it is
Water hammer Water hammer is a sharp banging or knocking sound in the pipes caused by a shock wave that forms when fast moving water is stopped suddenly, usually by a valve, toilet fill valve, or appliance closing quickly.
It is not an emergency, but repeated hammering stresses pipe joints and fittings over time and should be corrected before it causes a leak.
The short answer
Banging pipes are usually water hammer. When a valve closes quickly, moving water slams to a stop and the shock travels back through the piping as a bang. The common causes are waterlogged air chambers, missing or failed water hammer arrestors, house pressure set too high, and loose pipe straps that let the pipe move. It is worth fixing, because repeated shock loosens joints and eventually splits fittings.
What it usually means
These are the causes we find most often, ranked from most likely to least.
- 1
Waterlogged air chambers
Most likely
The air cushion that absorbed the shock has filled with water and no longer works.
- 2
Missing or failed water hammer arrestors
Common
Fast closing appliance valves need a dedicated arrestor nearby.
- 3
House pressure too high
Common
High static pressure makes every shock harder. A pressure reducing valve is the fix.
- 4
Loose pipe straps or unsupported runs
Less common
The pipe knocks against framing rather than the water itself hammering.
- 5
Failing fill valve in a toilet
Occasional
A valve that slams shut creates the shock every single fill cycle.
What to do right now
- 1Shut off the main, open the highest and lowest faucets to drain the system, then restore water to recharge air chambers.
- 2Note which fixture triggers the bang. That narrows the source quickly.
- 3Have static pressure checked if the banging is house wide.
When it is an emergency
- A banging pipe is followed by a visible leak or a wet ceiling.
- The noise starts after a pipe repair and pressure seems unusually high.
What the fix involves
The fix pairs pressure control with shock absorption. Where pressure is high, a pressure reducing valve is installed or replaced. Arrestors go in near the fast closing valves, and loose runs get strapped so the pipe cannot move against framing.
- 1Measure static pressure at the hose bibb.
- 2Drain and recharge the system to clear waterlogged chambers.
- 3Install arrestors at washing machine, dishwasher, and toilet connections.
- 4Replace the pressure reducing valve and secure loose piping runs.
What drives the cost
Every job is quoted before work begins. These are the factors that move the number on this kind of repair.
- Number of arrestors required and where they must be installed
- Pressure reducing valve replacement
- Access to piping in finished walls or ceilings
Related problems homeowners ask about
Why are my pipes whistling?
A high pitched whistle or squeal when water runs, sometimes only at partial flow or only when a toilet refills.
Read this nextWhy is water pressure low in my whole house?
Weak flow at every tap, showers that lose force when another fixture runs, and appliances that take much longer to fill.
Read this nextWhat do I do when a pipe bursts?
Water spraying or pouring from a pipe, a sudden pressure drop, water running down a wall, or a ceiling bulging and dripping.
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Licenses, credentials, and company proof
- Colorado Master PlumberLicense MP-18927
- Colorado State Plumbing ContractorLicense 2110
- Family Owned & OperatedServing Denver since 2006, 20 years
- Better Business BureauAccredited Business, A+ rating
- Angie's List Super Service Award2012 through 2017
- Serving Denver since 2006Residential and commercial properties across the metro
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Straight answers on what banging pipes and water hammer work costs, how fast we can get out, and what stands behind the repair.
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