Why do my pipes knock when multiple faucets are running?
Water hammer happens when fast-moving water suddenly stops, causing pressure shockwaves that rattle pipes throughout the house, often triggered by appliances, multiple running faucets, faulty pressure relief valves, or cheap shower diverters. This knocking persists even after draining and refilling the lines, making it difficult to pinpoint whether the issue stems from a specific fixture or overall home water pressure.
What the numbers show
Counted from the threads quoted below. How we count
- This comes up 27.1× more often in r/HomeImprovement than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Installing water hammer arrestors at risers or directly at appliances like washing machines and dishwashers
- 2Checking shower diverters and ensuring valves are wide open
- 3Securing loose pipes
- 4Replacing a faulty pressure relief valve
- 5Running all faucets to get air out of the system
- 6Turning off the main water supply, draining all water until nothing flows, slowly reopening the main, and turning faucets back on from the bottom up
- 7Flushing dirt out of the lines
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“I’m dealing with some water hammer on my domestic cold and hot water, almost all the appliances cause some form of hammering some more minor than others.”source ↗
“I had water hammer and found out one cheap shower diverter was causing it.”source ↗
“I had a pressure relief valve go bad on me.”source ↗
Where this came up
People with this problem also raised
- 3Why does my basement sink gurgle when the kitchen sink drains?
- 84How to fix a leaking water pipe in a tight space
- 30Why does my new plumbing still have bad water pressure and risky joints?
- 2How to deal with failing and rusted galvanized pipes
- 3Why is my tap water suddenly rusty and full of sediment?
- 7Busted a pipe trying to fix a drain