Installing a Thermal Expansion Tank on an Electric Water
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.
WARNING! Do Not Cap or Plug the Temperature and Pressure
Relief Valve Discharge Pipe. Explosion Hazard.
IMPORTANT - Read and follow the printed
Installation Instructions that came with your water heater. The
printed Instructions and product labels contain model-specific
information, important warnings and safety notices. If you lack the
necessary skills to install, troubleshoot or repair the water
heater, get help from a qualified person.