Pipes banging in the walls

Banging pipes are most often water hammer, the shock you hear when moving water is stopped fast, but loose pipes and high pressure can make the same noise. Let's sort it by when the bang happens and whether it is one fixture or the whole house.

Also searched as: pipes banging in walls, pipes banging when water turned on, water hammer.

Before you start. If you smell gas, leave and call 911 and your gas utility from outside. If water is leaking, shut off the main water valve by hand and never force it. Ready.gov says not to touch electrical equipment if it is wet or if you are standing in water.

Every question and answer on this page, in order

Question 1: Do you smell gas, or see leaking water, a damp wall or a ceiling stain?

Check around the water heater and below the noisy pipes, and look at nearby walls and ceilings.

I smell gas, a rotten-egg odor, or I'm not sure: Leave now: possible gas leak
I see leaking water, a damp or stained wall or ceiling, or a wet floor: Call a plumber: banging with water where it should not be
No gas smell and no water where it should not be: go to question 2

Question 2: When do you hear the noise?

Think about what you did just before it started.

At the water heater: rumbling, popping, hissing, or water from the relief valve pipe: Call a plumber: noise at the water heater
Right after water stops, such as a faucet closing or a washer, dishwasher or toilet finishing its fill: go to question 3
When I turn water on, or while hot water is running: Likely cause: loose or moving pipes
It knocks, ticks or hisses on its own, with every tap and appliance off: Call a plumber: noise with no water running

Question 3: Is the bang at one fixture or appliance, or all over the house?

Close a few different faucets, one at a time, and listen. Note any appliance that bangs when it stops filling.

Mostly one fixture or appliance: Likely cause: water hammer at one fixture
Many fixtures, or the whole house shakes: Call a plumber: banging all over the house

Possible results

Need the words for the phone call? Build a what-to-tell-the-plumber checklist, or read when to call a plumber.