Water heater dip tube: what it does and how to tell it's broken

What the dip tube does

A. O. Smith's service handbook explains that when a hot water faucet is opened, water pressure forces cold water into the water heater through the dip tube, and that pushes hot water out of the tank. Rheem describes its replacement part the same way: a polypropylene tube that directs cold water to the bottom of the tank before it rises to the top.

Hot water floats on cold, so a working tube keeps the incoming cold water at the bottom, where the burner or lower element heats it. If the tube breaks short, cold water lands near the top outlet and you get a cooler shower long before the tank is actually used up.

Signs of a broken dip tube

• Hot water runs out early or turns lukewarm. A. O. Smith's troubleshooting chart lists a cracked, missing or short dip tube under both "Too Cold" and "Not Enough Hot Water".
• White particles in faucet screens and appliance filters. The same chart lists a crumbling dip tube as one cause of white particles. Mammoth Community Water District says an aging tube can send brittle white pieces into the hot water, from small pebbles to longer shards.
• Weaker hot water flow than cold. The American Water Works Association, quoted in 1999, pointed to a clear difference in pressure between the hot and cold taps.

Running out fast has other causes too, such as a failed element or sediment. Our guide to hot water that runs out fast covers them.

Check the particles: float or sink

The water works association's checks are simple. Pull the hoses off the washing machine and look for white or gray particles. If they're only in the cold line, they're probably not from the dip tube. If they're in the hot line or in faucet screens, drop them into standing water: pieces that float are from the dip tube. Heat is a second test, because dip tube plastic melts and smells like burned plastic.

Mineral scale behaves differently. It's hard and sandy and sinks to the bottom. Our cloudy hot water guide explains how scale forms as water is heated.

A. O. Smith's hot water test

A. O. Smith's Bulletin 36 gives a test for electric heaters that separates a dip tube problem from a normal tank. In short:

1. Time how long it takes to fill a 1-gallon bucket at the faucet nearest the heater. 12 seconds is 5 gallons per minute, 15 seconds is 4, 20 seconds is 3.
2. Set both thermostats to 130°F, run about 15 gallons of hot water, and let the heater recover. It should take roughly 45 minutes.
3. Measure the hot water with a candy thermometer. It should read 120°F to 140°F.
4. Keep running hot water until 60% of the tank is used: 24 gallons on a 40-gallon tank, 30 on a 50-gallon tank.
5. Measure again. It should be about 30°F below the first reading.

If it dropped by more than 30°F, A. O. Smith says to check the lower element and the dip tube. The thermostats sit behind panels next to live wiring, so switch the breaker off before opening them, or have a plumber run the test. Our guide to a bad electric water heater element covers the element side.

The bulletin also notes that newer heaters ship with shorter dip tubes, to stop hot water stacking at the top, and lower factory settings. Both reduce how much hot water a tank delivers, so a new heater can feel smaller than the one it replaced even with nothing wrong.

The 1993 to 1996 dip tubes

In 1999 the American Water Works Association said up to 90% of residential water heaters built between 1993 and 1996, an estimated 21 million, may have had a defective dip tube. Those polypropylene tubes broke down and sent plastic to faucets and appliances. A heater from those years would now be about 30 years old and well past a normal life, so any that remain are replacement candidates anyway. Our guide to reading the serial number shows how to check the date.

Coeur d'Alene, Idaho is one place where the housing is that age: the median home there was built in 1994 (see our Coeur d'Alene page).

The fix

The dip tube sits under the cold water inlet on top of the tank and can be replaced without replacing the heater. The water works association's advice was that this isn't a job for the average homeowner. The tank has to be fully flushed to remove the old pieces, and faucet strainers and aerators may need cleaning several times until all the chips are gone. See how to flush a water heater.

Use the part made for your heater. Bradford White, for example, fits its top-connect residential heaters with a cold-water delivery tube called Hydrojet, which uses a series of jet ports to reduce sediment buildup. Sediment matters more where water is hard. Nampa, Idaho's 2025 water report lists hardness up to 7.08 grains per gallon (see our Nampa page).

If the heater is old or the tank is already leaking, a new tube is money spent on a tank near its end. That's when replacement is the better call.

Local pages mentioned

• Nampa, ID
• Coeur d'Alene, ID