Installing a Thermal Expansion Tank on a Gas Water Heater

When water is heated, it expands. In older homes, the expanded water pushed back into the water main. Today, most homes have backflow prevention valves which stop the water in your home from reentering the water supply. These valves can be inside water softeners, pressure regulating valves or the water meter itself. Backflow prevention valves (also known as "check valves") prevent the expanded water from reentering the water main. Since the expanded water now has nowhere to go, the water pressure in the house's pipes can increase dramatically, often to the point where the Temperature and Pressure Relief Valve discharge pipe drips. A thermal expansion tank has an internal air bladder which can absorb the expanded water, protecting plumbing, appliances and the water heater. For these reasons, most homes now need a thermal expansion tank (and a properly adjusted pressure regulating valve). Not having a thermal expansion tank is the most common reason for a dripping discharge pipe.

View The Printable Guide (PDF)
"Replacing the Thermal Expansion Tank"

WARNING! Do Not Cap or Plug the Temperature and Pressure Relief Valve Discharge Pipe. Explosion Hazard.