If you have an expansion tank and the pressure increases when the water heater is heating water, the expansion tank's rubber bladder may have failed, the tank may have the wrong air pressure, or it may be too small for your home.

Thermal expansion happens in your car, too. The water in your car's engine expands when heated. The expanded water is collected in an expansion tank or reservoir and is held until the engine cools down.

Expansion tanks come with a chart that will help you determine the size needed for your home. If in doubt, get the larger size.

The information on this web site is supplemental to the printed instructions that came with your water heater. To reduce the risk of property damage, serious injury or death, read and follow all labels on the water heater and the safety instructions in the printed owner's manual.

Add air to the expansion tank (using a bicycle pump or air compressor) until the air pressure in the tank matches the home's water pressure.

In years past, water heaters were installed on "open" plumbing systems which allowed the increased pressure to push back into the public water system.

The air pressure charge and the rubber bladder give the expanded water a place to go. This prevents the home's water pressure from increasing dramatically during a heating cycle.

To reduce pollution, most plumbing systems are now "closed." Today, when cold water in your water heater is heated and expands, it dramatically increases the pressure in your home's pipes which can damage your home's plumbing system.

If your home's normal water pressure is 60 psi, thermal pressure caused by heating cold water can increase your home's water pressure to 120 psi or higher.

Expansion tanks should be attached to the cold water pipe. Typically, expansion tanks are located near the water heater, but can be placed on a cold water pipe anywhere in the home if there are no valves in between.

Don't replace a dripping Temperature and Pressure Relief Valve until you've controlled your home's water pressure and installed a Thermal Expansion Tank.

Residential Thermal Expansion Tanks are available in 2 gallon and 5 gallon capacity. Larger water heaters require a larger expansion tank.

If your old water heater leaked prematurely, check your home's water pressure with a pressure gauge (available at hardware stores and home centers for a few dollars). Measure the water pressure over a 24-hour period. (Water pressures are highest at night.)

Plumbing codes require that your home's water pressure be 80 pounds per square inch (psi) or less. Most experts recommend 50-60 psi.

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