What Causes Hot-Water Faucet Hammering?

Attach a garden hose to the drain spigot to avoid leakage on your floor.

Water hammer, a rhythmic banging noise produced when you shut off a tap, can damage plumbing if you ignore its audible warning signs. When using the hot-water tap, water rushing too quickly through your pipes between the water heater and the tap can cause water hammer when the tap closes, as water continues to rush and slam against the valve and pipework. Most plumbing systems contain air pockets designed to cushion excess water pressure and stop water hammer. Over time, these air pockets may leak or be siphoned off through excessive water pressure. In many cases, all you need to do is refill air cushions to stop water hammer when using your hot water.

Things You'll Need

• Garden hose
• Pipe wrench
• Standard screwdriver
• Putty knife
• Pipe cleaner
• Plumber's tape

Instructions

1. Shut off the water supply to the hot-water heater by closing the feed valve, which is usually a ball valve located on the pipe feeding into the water heater’s top. If both lines are fitted with valves, carefully touch each pipe to determine the cold-water feed. Shut off the cold-water supply.

2. Affix a garden hose to the drain spigot at the bottom of the water heater. Place its open end in a sewer line or outdoors to allow it to drain without damaging your floor.

3. Open all hot-water taps in the home to help ventilate the plumbing and allow air to return to cushion sections. Because the valve is closed on the hot-water heater’s feed line to kill street-side water pressure, expect only a drizzle from the pipes. Open the hot-water heater’s drain spigot and allow the heater to partially drain. You don’t need to drain the heater entirely, but merely drain it low enough so air gets in the tank.

4. Close all hot-water taps as well as the drainage spigot on the hot-water heater. Once the system is closed, open the valve on the feed line so that the heater’s tank can refill. Allow the tank to refill completely, then turn on an upper-floor hot-water spigot to ensure you have water pressure. Test the faucet for water hammer. If it continues, proceed to Step 5.

5. Repeat Steps 1 through 3 drain the hot-water system. Locate the air cushion installed on your hot-water system. Cushions are typically larger-gauge pipes fitted on the upper end of a three-way elbow and are capped closed.

6. Remove the air-cushion pipe’s cap using the pipe wrench. Using a pipe cleaner, putty knife or standard screwdriver, clean out calcification and other deposits that may clog the opening to the air-cushion section. Once you remove the accumulation, replace the cushion’s cap using plumber's tape and a pipe wrench to ensure a tight seal.

7. Close the faucets and hot-water-drainage spigot and allow the hot-water heater to refill by opening the valve on its feed line.

Tips & Warnings

• Water hammer is a specific, rhythmic banging caused when faucets are shut off. If your hot-water faucet makes another type of noise while in operation, you may need to insulate your pipes to stop them from contracting when they cool or tighten harnessing that holds pipes so they don’t bang together or against walls when the plumbing’s in use.

• Depending upon your settings, water drained directly from your water heater may be very hot and may scald if it comes into contact with skin.

References

• Irrigation Tutorials: Water Hammer and Air in Pipes
• Building a Dream: Water Hammer
• A Plumbers: Noisy Pipes
• Handyman USA: Q&As on Noisy Pipes

Resources

• The Plumber: Plumbing Care & Repair Handbook