Leak in Line That Is Going to the Expansion Tank on a Hot Water Heater

Expansion Tank Purpose

• The simple purpose of an expansion tank on a water heater is to provide an outlet for water that expands when heated. This is a very basic principle of water chemistry, but is sometimes ignored in water heater design and installation. The implosion of the water molecules when water is heated creates a higher volume of liquid that must be displaced, or excessive pressure occurs within the water heater itself and along the plumbing lines connected to it. This increased pressure eventually leads to a plumbing leak somewhere in the system, including possibly the plumbing line feeding the expansion tank.

Expansion Tank Function

• An expansion tank functions by means of an internal bladder filled with air. The bladder compresses the air created by the heating of water as the heated water enters the expansion tank. This process prevents air from entering the water supply and, consequently, the water heater itself. Air is a common cause of increased water pressure, another cause of leaks in plumbing lines. A residential expansion tank generally holds 2 gallons of water, handles 150 pounds per square inch of pressure, and is best installed at a greater height than the water heater to enable proper drainage back into the water heater.

Expansion Tank Criteria

• Two factors determine the size and type of expansion tank required for your water heater: the capacity of the water heater and the water pressure serving your home. Both of these figures are found on the water heater, usually on a stamped or engraved label attached to the side of the heater. The water pressure is affected by the main supply line coming from the municipal supply or your well, and gauges to determine the pressure are available for purchase or are used by your local water department service staff.

Preventing Leaks in Plumbing Lines

• Several devices help control both the pressure and the temperature of the water as it moves through a water heating system, including the expansion tank plumbing lines. Pressure-reducing valves are fail-safe devices that remove excess pressure from a system, and a bypass feature should also be included with these valves to prevent leaks. A pressure-temperature safety valve is another useful device. Also consider including air separators, sometimes referred to as air scoops, in your system. These devices remove the air that is created naturally when water is heated, while preventing pressure buildup and corrosion, both of which eventually lead leaks in plumbing lines that service both the water heater and the expansion tank.