Quick answer
A water heater dip tube is a long plastic tube attached to the cold water inlet of a storage tank water heater that carries incoming cold water down to the bottom of the tank, so it is heated there and does not mix with the hot water drawn from the top.
A cracked, short or melted dip tube lets cold water mix in near the outlet, so hot water runs out early or comes out lukewarm.
Quick facts
The key facts about Water Heater Dip Tube, with sources:
Key takeaways
- The dip tube sends incoming cold water to the bottom of a tank water heater, where the heat is.
- If it cracks, melts or breaks off, cold water mixes in at the top and hot water runs out early.
- A.O. Smith warns that soldering pipes while attached to the heater can melt the dip tube.
- Bits of white plastic in faucet screens can point to a dip tube breaking down.
- A dip tube is a replaceable part; one bad tube does not mean the heater must be replaced.
What the dip tube does inside a tank water heater
Hot water rises and cold water sinks, and a tank water heater is built around that fact: it draws hot water from the top of the tank and brings cold water in at the bottom.
An inventor’s patent on tank design describes the goal: cold water is delivered to the bottom of the tank, because mixing with the heated water lowers the outlet temperature 5.
On most tanks, the cold inlet and hot outlet both sit on the top. The dip tube is what makes the cold water travel to the bottom anyway.
A.O. Smith’s manual calls it a long plastic tube inside the tank attached to the cold water inlet 1. Lennox says it is typically 30 to 40 inches long 3.
Some makers build extra features into the tube. Bradford White’s spec sheet describes a factory-installed Hydrojet system, a sediment-reducing device that it says also raises the first-hour rating 2. A.O. Smith’s parts list for one model shows a combined heat trap and dip tube on the cold side 1.
- Hot outlet zone (top)Hottest water leaves here
- Warm bandGradual change as water heats
- Cold zone (bottom)Dip tube releases cold water here, near the burner or lower element
A broken dip tube releases cold water near the top instead, cooling the water you draw. Source: [5] [1]
How cold water moves from the inlet to the tank bottom
- Cold supply line
- Shutoff valve
- Cold inlet nipple (often with a heat trap) 1
- Dip tube, down the inside of the tank 1
- Released near the tank bottom 5
- Heated by the burner or lower element
- Rises to the hot outlet at the top
- Out to your fixtures
Hot outlet vs cold inlet
A.O. Smith lists reversed hot and cold connections next to a melted dip tube as a cause of too little hot water, usually found soon after a new installation 1.
If the cold supply is piped to the hot port, the dip tube is on the wrong side and cold water never gets sent down.
Which dip tube materials and designs are used
| Type | What it is | Source |
|---|---|---|
| Plain polypropylene tube | Common in older and entry-level heaters; can turn brittle with hard water or tank temperatures above 140°F, per Lennox | 3 |
| Cross-linked polyethylene (PEX) tube | Lennox says it tolerates up to 200°F and resists scale better | 3 |
| Heat trap and dip tube combination | Inlet fitting and tube as one part, shown in an A.O. Smith parts list | 1 |
| Sediment-reducing tube | Shaped outlet that stirs the bottom, such as Bradford White Hydrojet | 2 |
| Rigid vs flexible replacement | Rigid is standard; flexible tubes can drift out of position, per Lennox | 3 |
Example: was your heater made during the defective-tube years?
A.O. Smith’s 2004 filing with the SEC says a supplier, Perfection Corporation, supplied defective dip tubes to water heater makers from August 1993 to October 1996 4.
Heaters that old are now about 30 years old, but some are still in service. Here is how the date check works, using the manufacture date on the rating plate.
| Manufacture date on the plate | Inside the window named in the filing? | What to do |
|---|---|---|
| June 1993 | No: before August 1993 4 | Diagnose symptoms as usual |
| March 1995 | Yes 4 | If water is lukewarm or plastic bits appear, have the tube checked |
| October 1996 | Yes, the last month named 4 | Same as above |
| May 1998 | No: after October 1996 4 | Diagnose symptoms as usual |
The filing names a supplier, not every brand, and says nothing about which models used its tubes, so a date inside the window is a reason to look, not proof of a bad tube. A tank of that age also has other wear; see our repair vs replace tool.
Where you see it, and where it shows up on a repair ticket
You cannot see the dip tube from outside. It sits below the cold water inlet on top of the tank, under the inlet nipple. On the diagram in the A.O. Smith manual it is labeled "Inlet Dip Tube," next to the cold water inlet 1.
It shows up on a repair ticket as "replace dip tube," often during a call about lukewarm water or a heater that runs out fast. Our water heater repair and replacement service page covers that kind of diagnostic visit.
Tankless heaters do not have one. Lennox notes dip tubes are found in gas and electric storage tank models 3. A heat pump water heater also stores water in a tank, so check its manual for its own inlet design.
What a working dip tube gives you, and what can go wrong
What it gives you
- Keeps the hottest water at the top where it is drawn off 5.
- Helps you get the full rated supply of hot water; Bradford White ties its tube design to first-hour rating 2.
- Some designs stir sediment at the bottom to reduce buildup 2.
- A cheap, replaceable part compared with the tank.
- Needs no adjustment once installed.
What can go wrong
Which hot water problems a new dip tube cannot fix
A new dip tube restores layering. It does not add capacity. If the heater is too small for your household, A.O. Smith lists that as its own cause of running out of hot water 1. Our water heater sizing tool checks capacity against demand.
It also does not fix sediment or scale in the tank bottom, which A.O. Smith lists as another cause of low hot water 1. Flushing the tank, not a new tube, is the fix for that. And it will not fix a hot water leak, a failed element or a gas burner problem.
Lifespan claims vary. Lennox says most dip tubes are built to last 8 to 12 years 3; we found no standard or independent study to confirm a figure, so treat it as one maker’s estimate.
What drives the cost of a dip tube repair
We do not list prices; fair numbers need dated local quotes.
The part is small. The cost is mostly labor and access: whether the heater must be partly drained, whether the cold inlet nipple is seized or corroded, whether the tube is part of a heat trap combination fitting, whether broken pieces must be flushed out of the tank, and whether faucet aerators must be cleaned.
If the heater is near the end of its life, a plumber may advise replacement instead.
Our plumbing cost guide explains how quotes are built.
How a plumber checks and replaces a dip tube
A.O. Smith says a melted dip tube can be replaced by removing the cold water inlet connection, removing the old tube and installing a new one 1. In practice the job runs like this:
- Turn off the energy: Power at the breaker for electric units; gas units go to the pilot or off setting per the manual.
- Shut off the cold supply and open a hot tap to relieve pressure.
- Drain some water so the level is below the inlet.
- Disconnect the cold inlet and remove the nipple or heat trap fitting 1.
- Pull and inspect the tube: Look for cracks, short length or melting.
- Install the matching part for that heater, then reconnect, refill with a hot tap open, and restore energy.
- Clean faucet aerators if plastic bits reached them.
Hot water and gas safety
Tank water is hot enough to scald, so let it cool or drain with care. Never turn a heater back on before it is full of water.
Leave gas connections, burners and venting to a licensed plumber, and if you smell gas, leave the home and call your gas utility or 911. Never cap or plug the temperature and pressure relief valve.
How to protect the dip tube
- Do not solder copper pipes while they are attached to the heater; A.O. Smith says this can melt heat traps or the dip tube 1.
- Keep the thermostat at a safe setting; Lennox says sustained tank temperatures above 140°F make polypropylene tubes brittle 3.
- In hard-water areas, manage scale; see our water hardness tool.
- Flush sediment as your manual directs, so loose debris does not clog screens.
- Use the maker’s replacement part so the length and fitting match.
Check the aerator
Unscrew a faucet aerator and look at the screen. White or gray plastic flakes, rather than gritty mineral scale, are the clue Lennox links to a dip tube breaking down 3.
Which signs point to a failing dip tube
- Hot water runs out noticeably faster than it used to 3.
- Water comes out lukewarm at a normal thermostat setting; Lennox gives 90–100°F instead of 120°F as an example 3.
- Small plastic fragments in faucet screens or showerheads 3.
- Temperature swings during one shower 3.
- Low hot water right after a new installation, which A.O. Smith links to a melted tube or reversed connections 1.
- Read hot water at the nearest tap with a thermometer; Lennox gives 90–100°F instead of about 120°F as a dip tube sign 3
- Unscrew a hot-side aerator and look for soft white or gray plastic flakes, not hard gritty scale 3
- On a new install, confirm the cold supply goes to the cold inlet, not the hot outlet 1
- Ask whether pipes were soldered while attached to the heater 1
- Rule out sediment: a rumbling tank and gritty debris point there instead 1
- Check the heater size against your household’s demand 1
These symptoms overlap with a failed element, sediment and an undersized heater, so work through the checklist above before paying for parts. A plumber can test each cause in turn. For a leaking tank, see our plumbing emergencies guide.
Which rules and test procedures touch the dip tube
No plumbing code section we found regulates the dip tube on its own. It is an internal factory part of a listed water heater, covered by the maker’s design and instructions. Replacing it with the maker’s part keeps the heater as listed; check your warranty terms before using a generic part.
Federal efficiency testing: the DOE test procedure for water heaters (10 CFR 430, Subpart B, Appendix E) measures delivered hot water and first-hour rating on the heater as built 6.
Because the dip tube shapes how hot water layers in the tank, a broken one changes real-world delivery even though the rating on the label stays the same.
Permits: Swapping a dip tube is a repair, but replacing the whole heater often needs a permit; rules vary by city.
How the dip tube differs from heat traps, anodes and relief valves
| Part | What it does | Main difference |
|---|---|---|
| Dip tube | Sends cold water to the tank bottom 1 | Controls where cold water enters |
| Heat trap | Fitting on the inlet or outlet that limits heat loss through pipes | Some makers combine it with the dip tube 1 |
| Anode rod | Protects the steel tank from corrosion | A.O. Smith says one must be installed at all times or the warranty is void 1 |
| Drain valve | Lets you flush sediment from the bottom | Outlet at the bottom, not an inlet |
| T&P relief valve | Releases water if temperature or pressure get too high | A safety device; never cap or plug it |
Which dip tube beliefs are wrong
- Myth Lukewarm water always means a bad dip tube.
- Reality A.O. Smith lists several causes, including sediment, an undersized heater and leaks 1.
- Myth Plastic bits in faucets are always from the dip tube.
- Reality They can be; mineral scale and other debris also collect in screens. Look at what the flakes are made of.
- Myth Dip tubes only fail in old heaters.
- Reality A.O. Smith links a melted tube to soldering during installation, found soon after a new heater goes in 1.
- Myth Tankless heaters have dip tubes too.
- Reality Lennox notes they are found in storage tank models 3.
- Myth A failed dip tube means a new heater.
- Reality A.O. Smith describes replacing the tube itself 1.
Hard water and the dip tube
Water hardness is the local variable that matters most here. Lennox says hard water is one of the conditions that can make polypropylene dip tubes brittle and shorten their life 3.
Hardness varies a great deal from one water system to the next, so check yours before blaming age alone, and look for scale as well as plastic in faucet screens.
If your heater is in a garage or unheated space in a cold climate, also protect its supply lines from freezing.
When the dip tube matters to you
Suspect the dip tube when hot water runs out fast or comes out lukewarm and you also see plastic bits in faucet screens, or when the problem started right after a heater was installed with soldered connections.
The next step is a diagnosis that rules out the element, burner, thermostat and sediment. If the tube is the cause and the heater is otherwise sound, a tube swap is usually the smaller fix.
- If Plastic flakes in aerators and lukewarm water
- Then Likely dip tube; have it inspected 3
- If Problem began soon after a new install
- Then Melted tube or reversed hot and cold lines 1
- If Rumbling tank, gritty scale
- Then Sediment buildup 1
- If Hot water runs out with a big household
- Then Heater may be undersized 1
Questions about Water Heater Dip Tube
How can I tell if my dip tube is broken without taking it out?
Start with a thermometer and a faucet aerator. Lennox gives hot water arriving at 90 to 100°F instead of about 120°F, and soft white or gray plastic flakes in aerators, as signs of a failing tube.
If both show up and the heater is not new, a broken tube is likely. Sediment, a weak element and an undersized heater cause similar symptoms, so have a plumber confirm before buying parts.
What are the signs of a bad dip tube?
Common signs are hot water running out faster than before, lukewarm water at a normal setting, temperature swings during a shower, and small white plastic fragments in faucet aerators or showerheads. Lennox lists these as dip tube symptoms. Several other faults cause similar signs, so a plumber should confirm the cause.
Can a dip tube melt?
Yes. A.O. Smith’s manual says soldering copper pipes while they are attached to the water heater can melt the dip tube or the heat traps. The problem usually shows up soon after a new installation as too little hot water. The fix is to replace the tube.
How long does a dip tube last?
No code or standard sets a lifespan. Lennox says most are built to last 8 to 12 years, and that hard water and high tank temperatures can shorten that. We found no independent data to confirm a figure, so treat any lifespan as an estimate.
Can I replace a water heater dip tube myself?
A.O. Smith describes the job as removing the cold water inlet connection, pulling the old tube and installing a new one. It involves draining hot water and working on a gas or electric appliance, so many homeowners hire a plumber. Turn off the energy source first and never run the heater empty.
What were the defective dip tubes of the 1990s?
A.O. Smith’s 2004 SEC filing says Perfection Corporation supplied defective dip tubes to water heater makers from August 1993 to October 1996. Heaters made in that window may have had them. A date in that range is a reason to inspect, not proof of a bad tube.
Do tankless water heaters have a dip tube?
No. A dip tube exists to keep hot and cold water layered in a storage tank, and tankless heaters heat water as it flows through. Lennox notes dip tubes are found in gas and electric storage tank models.
Why is there plastic in my faucet aerator?
One possible cause is a dip tube breaking down inside the water heater and sending flakes through the hot water lines. Look at the flakes: plastic is soft and white or gray, while mineral scale is hard and gritty. If plastic shows up mostly on hot taps, have the dip tube checked.
Sources
- A.O. Smith, Residential Standard Gas Ultra Low NOx Water Heater Installation Instructions and Use and Care Guide (single manufacturer), retrieved .
- Bradford White, RG140T6X Residential Atmospheric Vent Gas Water Heater specification sheet (single manufacturer), retrieved .
- Lennox, What Is a Dip Tube in a Water Heater? (September 1, 2026; manufacturer consumer article), retrieved .
- A.O. Smith Corporation, press release filed with the U.S. SEC as Exhibit 99 (July 13, 2004), on dip tube litigation, retrieved .
- U.S. Patent 5,054,437, Storage tank for water heaters and the like with collector outlet dip tube (H. D. Kale, 1991; Google Patents), retrieved .
- 10 CFR Appendix E to Subpart B of Part 430, Uniform Test Method for Measuring the Energy Consumption of Water Heaters (Cornell LII), retrieved .
Expert review
Written by the HyrePlumber Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Function and failure causes are from A.O. Smith’s installation and use guide and a 1991 tank-design patent. Materials, typical length, symptoms and the lifespan estimate are from a Lennox consumer article, labeled as one maker’s view.
The 1993–1996 defect window is from A.O. Smith’s 2004 SEC filing; trade-press reports on the settlement could not be loaded and are not used. The DOE test procedure was checked for scope only. No prices are given.
Suggest a correction. We fix errors and say what changed.