While there are lots of causes for hot water problems, one of the lesser-known troubles is dip tube failure. If you are experiencing a significant loss in hot water temperature or pressure, then this might be the source of trouble. Here is more information about dip tubes, what happens when they fail, and what you can do about it:

Dip tubes explained

Hot water heaters are fairly simple devices that operate according to basic physics principles: cold water is heated at the bottom of the tank by a burner or electrical coil, and it rises toward the top where it is expelled from the tank as hot water. If the cold water is mixed with hot water inside the tank, you will receive tepid water when you turn on the faucet.

Hot water heater designers overcome this problem in one of two ways: they either pipe cold water directly into the bottom of the water heater, or they send it down from the top of the tank through an internal pipe known as a dip tube. The dip tube runs all the way to the bottom of the water heater where the cold water is released. This preserves the proper arrangement by creating a thermal layer of cold water on the bottom and a layer of hot water at top.

You can tell if your hot water heater is a dip tube-equipped unit if you see two water lines entering the top of your tank. One line at the top, and one line at the bottom indicate your heater has a bottom cold water intake.

Why dip tubes fail

Dip tubes are usually constructed of cross-linked polyethylene (PEX), a type of heat-resistant plastic. Dip tubes are fabricated to withstand the consistently hot temperatures inside a hot water heater. However, in time, even a heat-resistant PEX tube is likely to break down inside its unforgiving environment. Once it begins breaking down, tiny fragments of PEX will spread throughout your hot water heater and into the hot water lines of your home.

Know the symptoms of dip tube failure

The classic symptoms of dip tube failure—lukewarm water at the faucet and low water pressure—are produced in response to the breakdown of the plastic. When the tube cracks or disintegrates toward the top end of the tank, cold water escapes through the holes and cools the hot water to a tepid temperature. Occasionally, dip tubes will break free completely from their connections, and this will also result in lukewarm water production.

When water pressure lessens on just the hot water side, you should also suspect dip tube failure. The small fragments of PEX flow through pipes and lodge in the supply valves of sinks and bathtubs. These pieces can be caught inside shower heads and kitchen faucets strainers, as well. Eventually, the plastic residue will create a clog, and potentially block your hot water flow nearly altogether.

How to diagnose dip tube failure

Your first step to diagnosing dip tube failure is a simple task: simply remove the strainers from your sinks and your shower heads. The presence of tiny white pieces of plastic inside your strainer or shower head is a tell-tale sign. However, if you don't see any pieces of plastic, don't assume your dip tube is intact. In some circumstances, the pieces of dip tube never make it all the way through into your plumbing fixtures. Here is another test you can perform if you still suspect dip tube breakdown:

  1. Locate the hot water valve and hot water hose that leads into your washing machine.

  2. Completely close the hot water valve by turning it all the way to the right.

  3. With a pair of pliers or a plumber's wrench, unfasten the hot water hose from the back of your washer.

  4. Place the free end of the hot water hose into a kitchen strainer, and hold it over an empty five-gallon bucket.

  5. Slowly and carefully turn on the hot water valve until the water begins flowing at a moderate rate from the hose, through the strainer, and into the bucket. Be careful not to scald yourself.

  6. Allow the water to flow through the kitchen strainer until the bucket is full, and turn off the water.

  7. Look inside the strainer for signs of small pieces of PEX; they may be small, so look carefully.

What to do if your dip tube has failed

If the symptoms of dip tube failure and your tests show signs of tube breakdown, then you will either need to replace the tube or hot water heater. In most instances, a complete replacement of your hot water heater is often warranted, especially if your unit is several years old. Installation of a new dip tube is also a possibility, but it can be a difficult task for the do-it-yourselfer. Your best option is to contact a plumbing service, and explain your situation. They can provide an estimate regarding the cost of dip tube replacement as well as provide a price for a new water heater and installation.