Symptoms
- Loud bang or thud in the pipes when a faucet or appliance valve closes
- Noise seems to come from the pipes near or leading to the water heater
- Banging is sudden and brief, not continuous
- Happens most with quick-closing valves like washing machines or dishwashers
Likely causes
- CommonWater hammer from fast-closing valves elsewhere in the houseA moving column of water stops abruptly and sends a shockwave through the pipes, which can resonate near the water heater.
- CommonMissing or waterlogged water hammer arrestorsThese small shock absorbers near washing machines and dishwashers can fail or were never installed.
- PossibleLoose pipe straps allowing pipes to bang against framingPipes that aren't well secured can knock against studs or joists when water flow changes suddenly.
- PossibleHigh water pressure amplifying the effectExcess household water pressure makes water hammer more forceful.
What to do
- Note exactly when the bang happens, such as right when the washing machine fills or a faucet shuts off.
- Check if the noise happens throughout the house or seems isolated to pipes near the water heater.
- Look for exposed pipes near the water heater and see if they're securely strapped to framing.
- If a specific appliance triggers it, consider having a water hammer arrestor installed near that fixture's supply valve.
- Check your home's water pressure with a simple gauge screwed onto an outdoor spigot; over 80 psi may warrant a pressure-reducing valve.
- Secure any loose pipes you can safely access with additional pipe straps or padding.
Tools and parts
- Water pressure gauge
- Pipe straps
Water hammer arrestorSearch: “water hammer arrestor washing machine”
When to call a pro
If pressure is high or the banging is severe and frequent, a plumber can install arrestors, secure pipe runs, or add a pressure-reducing valve.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.