How to Replace a Faucet Backflow Preventer

A faucet backflow preventer prevents contaminants from flowing into the safe drinking water. Faucets, especially those found outside the home, are prone to contamination, most commonly if they are connected to a water hose. To avoid the backflow of contaminated water, a device called the faucet backflow preventer has to be installed in between the main water supply pipe and the faucet. This device gets leaky or damaged after long periods of use and should be replaced to ensure water safety.

Tools and Materials

  • Wrench or Vise
  • New Backflow Preventer
  • Dry Cloth
  • Pipe Dope

Step 1 – Shut off the Water Supply

Locate the water shut off valve that controls water flow to the faucet. If the faucet is not connected to a shut-off valve, find the main water supply switch and turn it off temporarily. Be sure no one switches the water on during replacement to avoid problems.

Step 2 – Remove the Old Backflow Device

Locate the backflow device in the water system and remove any objects that may be hiding it. The threads of the device are sealed with pipe compound so use a vise or a wrench to loosen the connections. Remember to turn the connection loose in a counterclockwise direction. Doing the opposite may damage the threads on the water supply pipe. Be sure to detach the device from the faucet as well. Clean the threads with a piece of cloth to remove any trace of the compound.

Step 3 – Purchase a New Backflow Preventer

Take the device to a plumbing store and purchase a new one. Make sure that the replacement has the same features or better. Check if the size is just enough to fit into the vacated slot in the water system.

Step 4 – Install the Replacement

Read the manufacturer’s instructions in the manual to ensure that any specific procedures are followed before installation. Check for the directional arrows on the device to know exactly which end connects to the faucet and which one connects to the water supply pipe.

Clean the pipes first to get rid of rust, oil, dirt or debris. Rub them dry with a cloth. Apply pipe dope on the male threads of the main water supply pipe. Insert the correct end of the backflow device into the pipe. Align the threads properly and hand-tighten. Use a vise or wrench to ensure a tight fit. Refrain from overly tightening the connection to avoid damage.

Afterwards, connect the other end of the device to the faucet or to the pipe that leads to the faucet. Apply pipe dope to the male threads as well before tightening the connection. Allow the pipe dope to cure for a period of time. Read the manufacturer’s instructions for recommended waiting time details.

Step 5 – Turn on the Water Supply

Make sure that the water supply is turned on only if the pipe dope has fully cured. This avoids any possibility of leaks occuring after installation. Turn on the water supply and inspect the device for any sign of dripping.