How to Troubleshoot a Leaky Water Heater

Fixing leaks from a water heater boils down to where the leak is located. These troubleshooting steps will help you determine if you need to repair the water heater, call in a professional to help, or replace it entirely.

1. Look at the Water Supply Lines

   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 the leak is coming from the tank itself.

   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 these tubes to fail long before the water heater is ready for replacement. If there is insulation around the supply tubes, remove it so you can inspect and replace the tubes if necessary.

   To replace the water heater flex lines, shut down the heater first by turning off the gas (for gas heaters) or the electricity (for electric heaters) running to the heater. For gas heaters, the instructions to turn the gas valve to the off position are typically on the front of the tank. For electric heaters, you can usually use a disconnect switch at the heater or a separate breaker to turn off the power.

   Next, 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.
   

   Warning

   If you aren't familiar or comfortable working with your heater, call a professional—and remember that only licensed professionals should work on gas piping.

2. Inspect the Water Heater Nipples

   The water heater nipples on top of the water heater, which connect the water heater to the cold water inlet pipe and to 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 are still observing leaking water, 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 to shut off the water and verify that it is off before doing this repair. In most cases, this is a job for a professional, as incorrect removal can cause many issues.
   

   Tip

   In some 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.

3. Look at the Temperature & Pressure Release Valve

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

   If the valve was removed recently, it's possible it is now failing to seal properly. Tightening the valve, or reinstalling it with fresh plumber's tape wrapped around the threads, may solve the problem.

   If the water heater is heating the water too much, the excessive pressure may be causing the T&P valve 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&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&P valve that needs replacing. Before replacing the valve, make sure the water is turned off and that there is no pressure in the tank. You can release pressure by opening the lever on the T&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.
   

   Warning

   Always be aware that you're working with very hot water under pressure. Take proper precautions. Experts strongly recommend calling a professional for repairs as many things can go wrong. Gas appliances should always be fixed by licensed experts.

4. Check the Drain Line

   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 valve. You will have to shut off the hot water and drain down the water heater before removing and replacing this valve.
   

5. Examine the Tank

   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 it must be replaced.