Bulging Water Heater and Leaking Problem: Can It Be Fixed?

Discover why a bulging water heater is a serious and potentially dangerous problem that can impact your home and safety. This article provides a guide on how to check for signs of a deformed tank caused by increased pressure in the tank, and what steps to take to resolve the issue. Additionally, you can learn about the common symptoms and causes of bulging and how to prevent it from happening in the future.

Plumbing tools to fix water heater problems
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What Causes a Bulging Water Heater and Is It Dangerous?

Common Reasons for Bulging

There are several reasons why a water heater may be bulging, and it’s important to address the issue promptly to prevent potential hazards like leaks, fires, or explosions. Here are some common reasons:

  1. High water pressure: If the water pressure in your home is too high, it can cause the tank to bulge. This is because the tank is designed to withstand a certain amount of pressure, and if it exceeds that limit, the tank can deform.
  2. Sediment buildup: Over time, sediment can accumulate at the bottom of the tank, causing it to overheat and weaken. This can result in bulging, as the weakened tank cannot contain the pressure of the hot water.
  3. Temperature and pressure relief valve malfunction: The temperature and pressure relief valve is designed to release excess pressure and temperature from the tank. If the valve is not functioning properly, pressure can build up inside the tank, causing the problem.
  4. Overheating: If the thermostat on your water heater is set too high, the water inside the tank can overheat, and affect the tank’s functionality.

High Pressure as the Cause of Bulging

A bulging water heater can be a serious and dangerous problem, caused by excessive pressure inside the tank. Common symptoms include dislocated flue pipes and pipe fittings, leaking, and permanent deformation. Signs of a bulging tank can be seen in the form of cockeyed nipples at the top and bulged or reversed bottoms of the heater’s head.

Tank-type water heaters are designed and tested to withstand maximum internal pressures of 300 psi without any distortion. If there is a deformation of the tank, such as a bulged bottom, it means the heater was subjected to pressures above 300 psi. The maximum working pressure for which the heater is designed is 150 psi.

When cold water is heated in the tank, the volume and pressure increase due to the expansion of water. For each 10°F increase in temperature, water expands by 0.2%. If the temperature increase causes the maximum designed pressure to be exceeded, the water heater can bulge and deform.

To learn more about bulging water heaters and how to fix them, refer to the technical bulleting from the AO Smith manufacturer. If you suspect your water heater is bulging or deformed, contact a licensed plumber immediately to assess the situation and recommend the best course of action.

How to Avoid Excessive Pressure Increase and Prevent a Bulging Water Heater

If your heating system is an open system, and if there are no obstructions to reverse the flow, the pressure in the tank will always be closed to the cold water supply. The hot water will expand back into the cold water supply, and there will be no damage to the plumbing system. In this case, the chances for a bulging water heater are minimal.

If there are obstructions, such as installing the checking valves, pressure reducing valves, shut-off valves in the cold water line, or water softeners, the system becomes a closed system. This will result in the rapid pressure increase of the heated water until something fails or ruptures. 

This is why the expansion tank must be installed to accept additional water and pressure.

If the expansion tank is not installed, the pressure may become extremely high, resulting in the water heater bulging, even tank rupture. This is why a good quality and reliable product should be selected.

The correct size of the expansion tank should be used on every new installation so it can maintain a consistent and safe working pressure. Keep in mind that the warranty will be voided, so whatever happens to the unit, it will be at your expense.

How to Test Hot Water Pressure Inside a Tank

One reason why your heater might be leaking is due to pressure buildup or a significant drop inside the tank. This is a simple DIY project that only requires a gauge. A leaking water heater can create a puddle on the floor, indicating a crack or hole in the tank or dislocated plumbing connections or unions. Follow the guide below to check and test hot water pressure:

  • To get a pressure reading inside the tank, install a gauge on the drain valve outlet and open it.
  • Close the main shut-off valve that is supplying the unit.
  • Make sure all hot water taps are turned off. When the heater is working and the hot taps are closed, the pressure will build up in the tank.
  • Run the heater by turning the thermostat up until the main burner or heating element comes on. Continuously check the gauge as the pressure in the tank will increase rapidly.
  • When the hot water pressure starts to rise, shut off the heater by turning the thermostat down. Watch the gauge to see if it holds pressure or drops off significantly.
  • If there are no leaks around fittings when the pressure drops, then the tank is leaking.
  • If the pressure inside the heater cannot rise, it could be because the hot water faucet is open in the system, or there is a hole or crack in the tank that’s preventing the pressure buildup.
  • If the pressure holds for an extended period (10-15 minutes), the tank is not leaking.

The typical design of the tank features convex top heads and concave bottoms. Due to excessive pressure inside the tank, the concave bottom might flatten or change to a convex or bulged shape. This is particularly dangerous on gas models, as the movement of the bottom can result in deformation of the tank head as it connects to the rigid flue. This can cause restrictions in the venting of combustion products through the flue passage and chimney.


To ensure the safety of your home and family, it’s crucial to take any signs of a bulging water heater tank seriously. If you notice any distortion in the tank’s bottom when inspecting the combustion chamber, it’s important to replace the tank immediately and identify and correct the root cause of the problem. Keep in mind that heaters with bulging conditions are typically not covered by warranty due to improper installation.

Experts agree that it’s best to call the plumber as soon as possible to address the issue, rather than attempting a DIY repair. The real concern with a bulging water heater tank isn’t the bulge itself, but rather the reason why the tank bulged in the first place. If the safety relief valve was unable to release pressure for any reason, the tank will inevitably fail, and potentially even explode, putting your home and loved ones in danger.

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