Installing a Gas-Line Sediment Trap on a Water Heater

Hands and pipe wrench affixing a water heater gas line

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If you look at the natural gas pipe providing fuel to your gas-fired water heater, it should already have a sediment trap—a downward tee fitting in the pipe just before the inlet on the control valve. Natural gas can carry with it small bits of debris, and if this debris gets into the pilot light or main burner assembly of your water heater, it can shorten its life. For this reason, the Uniform Plumbing Code and most city building and safety codes require a sediment trap, which provides a place for that debris to fall into before it can pass into your water heater. Call your local building department if you have any questions about whether or not a sediment trap is required.

If your water heater doesn't have one, Installing a sediment trap is quick, cheap and easy. It is wise to install one if you are replacing the water heater, or if you want to bring your current water heater up to code.  

Tools and Materials You Will Need

  • Black iron tee
  • Short shoulder-length black iron nipple
  • 4" black iron nipple
  • Black iron cap
  • Transition fitting (male iron pipe to flare fitting) if your gas line is a flex pipe connection
  • Pipe-joint compound
  • Channel-type pliers

If the gas flex line to your water heater only barely reaches the control valve now, you may need to replace it with a longer flex line. Another option is to make some adjustments to the gas line so that it makes up the difference. A sediment trap should be installed as close as possible to the control valve, so plan accordingly. 

Make sure you are using approved flex pipe if replacing a gas line. The proper flex lines are called corrugated stainless steel tubing (CSST). You may also find corrugated copper products, but these are no longer allowed by code in many areas. Some time ago, it was discovered that the chemicals added to natural gas to give it an odor could cause copper to flake off, so its use in the gas piping is now discouraged. If your existing water heater has copper flex piping or flexible solid copper tubing,  it's a good idea to replace it now with a CSST flex supply pipe. 

Also, make sure you have some appropriate pipe joint compound to put on the threads. Collect everything before you begin.

How to Install a Sediment Trap

  1. Shut off and disconnect the gas: Turn the gas off, either at the water heater or the meter. Once the gas is off, disconnect the flex line from the control valve, using pliers. Then remove the flare connection that goes into the water heater control valve.
  2. Prepare the fittings: Prepare the black pipe fittings by applying pipe dope to the threads of the nipples and on the flare connection threads. You can get these ready one at a time as you connect them, but it is easier to do this all at once.
  3. Put the sediment trap together: Start with the short nipple. Screw the short nipple into the tee and tighten, using two pairs of pliers. Then, carefully thread the tee-and-nipple assembly into the control valve of the water heater. Over-tightening the nipple onto the control valve can crack it, so be very careful not to tighten it more than necessary. Next, screw the cap onto one end of the long nipple. Then thread the other end of the long nipple into the bottom of the tee. Lastly, screw the remaining flare adapter into the top of the tee.
  1. Connect the gas: Hook the flex line back onto the end of the flare fitting. Turn the gas back on and check for leaks. It’s that simple!

Now you have an approved gas sediment trap that can help keep you safer and prolong the life of your water heater.