Five Reasons a Water Heater Can Leak

Hot water heater
Monty Rakusen / Getty Images

Fixing a leaking water heater can range from the very easy to the very challenging. At the first sign of leaking, many people leap to the conclusion that the water heater must be replaced, but that's not always (or even usually) necessary. Many potential fixes are actually rather simple and inexpensive, and sometimes replacing a broken part can extend the life of the water heater for several years. Here are five things to look for when diagnosing the source of a leak and determining the proper fix.

  • 01 of 05

    Leaking at the Water Supply Lines

    Insulated water heater flex lines
    Aaron Stickley

    The first place to check is the plumbing pipes above the water heater. A drip from above can easily leak down on top of the water heater and even work its way down the insulation and make it look like a leak coming from inside the tank. This is why it is important to always look above the water heater first.

    Check the plumbing pipes above the water heater, using a stepladder, if necessary. Pay special attention to the water supply lines going into the water heater. These may be rigid pipe connections or flexible supply tubes. Flexible water supply tubes are the most common cause of leaks above the water heater since it is common for the tubes to fail long before the water heater is ready for replacement.

    If there is insulation around the supply tubes above the water heater, remove it so you can inspect and replace the tubes if necessary. To replace the water heater flex lines, first shut the water off to the water heater. This will be a shutoff valve on the cold water pipe leading to the water heater Before removing the water supply tubes, verify that the water is turned off by turning on the hot side of a faucet somewhere in the house to see if water continues to flow. If the water has been successfully turned off, no water should be flowing out of the water heater.

  • 02 of 05

    Leaking at the Water Heater Nipples

    Water heater nipples
    Aaron Stickley

    The water heater nipples on top of the water heater, which connect the water heater to the cold water inlet pipe and the hot water exit pipe, are another common place to find leaks. The threads are the thinnest part on the nipple and it is not unusual to find leaks in them. This can be hard to differentiate from a leak at a supply tube, but if you changed the supply tube already and it is still leaking, the nipple is a likely cause.

    Removing the water heater nipples can be quite difficult and will require a pipe wrench and some leverage. Make sure shut off the water and verify that it is off before doing this repair.

    Note: In many states, a special fitting called a dielectric union is required if the galvanized steel nipples are connecting directly to copper pipes. The dielectric unions prevent corrosion that occurs because galvanized steel and copper touching together creates a mild electrical charge.

  • 03 of 05

    Leaking at the Temperature and Pressure Relief (T-and-P) Valve

    Water heater Temperature and Pressure relief valve
    Aaron Stickley

    Another possible place for leaks is the temperature and pressure (T-and-P) valve. A leak at the T-and-P valve is a more serious situation and you will want to take the time to figure out the cause. A T-and-P valve will not usually begin dripping or leaking unless there is a problem. Several possible causes include:

    • If the valve was removed recently, it's possible it is now failing to seal properly. Tightening the valve, or reinstalling it with plumbers tape on the threads may solve the problem.
    • If the water heater is heating the water too much, the excessive pressure may be causing the T-and-P to leak. The solution might be to lower the water temperature or to install a water expansion tank if you don't already have one in your plumbing system. 
    • The leaking T-and-P valve may indicate the overall water pressure in your home is too high, and that the pressure regulator is not working properly. 
    • If the water pressure in the house seems normal and the water heater is heating normally, then you may have a faulty T-and-P valve that needs replacing. When replacing the valve, make sure the water is turned off and there is no pressure in the tank before making the repair. You can release pressure by opening the lever on the T-and-P valve, or by opening a hot water faucet somewhere in the house.

    If you believe there is still a problem or are unable to get to the bottom of the issue, call a professional plumber to help assess and remedy the situation.

  • 04 of 05

    Leaking at the Drain Line

    Water heater drain valve
    Aaron Stickley

    A leak in the drain valve at the bottom of the water heater is another common issue. After draining or flushing a water heater, it is common for the drain valve to fail to close completely. This drain valve can be capped with a hose cap, or you can replace the drain valve completely with a new and improved valve. You will have to shut off the hot water and drain down the water heater before removing and replacing this valve.

    Continue to 5 of 5 below.
  • 05 of 05

    Leak in the Tank

    Water heater leaking at the tank
    Aaron Stickley

    Finally, if none of the prior inspections showed a cause for leaking, then it is likely that the tank inside the water heater has gone bad. Normally this will be a major, flooding leak, not small dripping. If the tank has ruptured and is leaking, the water heater cannot be fixed and must be replaced.