Pipes & water supply

Pipe vibration or hammer only on the hot water side

Noise limited to hot water lines often points to a water heater component (like an expansion tank or check valve) rather than the general plumbing, and is worth checking there first.

Difficulty
Moderate
Time
30–60 minutes
DIY cost
$15–$50
Pro cost
$150–$400

Symptoms

  • Banging or vibration only when hot water is used or shut off
  • Cold water side is quiet under the same conditions
  • Noise may correlate with the water heater cycling on
  • Sound sometimes heard even without water actively running

Likely causes

  • CommonMissing or waterlogged thermal expansion tankAs water heats, it expands, and without a properly functioning expansion tank to absorb that, pressure spikes can cause banging.
  • CommonWater hammer arrestor missing specifically on hot supply linesIf arrestors were only installed on cold lines during past work, hot side hammer can still occur.
  • PossibleFailing check valve near the water heaterA check valve that's supposed to prevent backflow can chatter or bang if it's not seating properly.
  • Less commonLoose hot water pipe expanding and contracting against framingMetal pipes expand slightly when heated and can tick or bang against framing if not properly clipped.

What to do

  1. Check near the water heater for a small tank (thermal expansion tank), usually mounted on the cold inlet line; tap it to see if it sounds hollow (good) or solid (waterlogged).
  2. If waterlogged or missing and your water heater has a check valve or pressure-reducing valve (closed systems require one), consider having an expansion tank installed or recharged.
  3. Install hot-side water hammer arrestors at fixtures where the banging is most noticeable, following the same process as cold-side arrestors.
  4. Listen along accessible hot water pipe runs for a ticking sound as the water heater cycles, which points to thermal expansion against loose framing.
  5. Add or tighten pipe straps and add cushioning where pipes contact framing.
  6. If a check valve near the water heater is suspected, this typically requires a plumber to test and replace.
  7. Monitor water heater temperature settings, since excessively high settings can worsen thermal expansion effects.

Tools and parts

  • Wrench
  • Pipe straps
Thermal expansion tankSearch: “thermal expansion tank for water heater”

When to call a pro

Call a plumber to install or replace a thermal expansion tank or check valve near the water heater.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.