To whom it may concern;

Recently, I experienced a very frustrating situation involving a leaking water heater in the West Menlo Park home of a friend.

A 30 gallon Rheem gas water heater was originally installed in her home by a reputable plumbing company in July 2009. Cost including a 10% CAP rebate was $2,041. In 2011, my friend noticed water accumulating in the pan below the unit. A conversation with the plumber suggested that this was normal. Several months after notifying the plumber of the problem it became necessary to replace the water heater.

After replacement by the original plumbing company, water was still accumulating in the pan. They then contacted Rheem who agreed to provide another replacement for the ostensibly defective unit. Rheem dispatched another plumbing company to install this second replacement. A faulty installation of water connections required a second visit from the plumber. Subsequently, the T&P valve was observed to operate after hot water usage, causing water to again accumulate in the pan.

Seeking to ascertain the origin and magnitude of overpressure activating the T&P valve, I purchased a Watts pressure gauge and installed it on the water heater drain outlet. Peak pressure as high as 180 psi was recorded following hot water use. This could easily rupture devices not designed to withstand such extreme pressure. An online search resulted in a simple explanation of the problem. Thermal expansion. See: Code Restrictions on Thermal Expansion Control in Domestic Service Water Heating Systems by Dennis M. Streit: Web Link.

When apprised of the situation, Rheem’s chosen plumber offered to install a Thermal Expansion Tank for $200.

The problem of thermal expansion associated with water heaters occurs only in homes with “closed” systems created by pressure regulators and/or backflow preventers. Consultations with Cal Water revealed that the water main pressure delivered to my friend’s home was well in excess of 100psi. And, that her home has a pressure regulator installed to reduce that to a safe level of ~60psi.

I suggested a less expensive alternative to the Thermal Expansion Tank. A simple pressure relief valve located anywhere in the closed system could bleed-off the small volume of water produced by thermal expansion. Further searching of the Internet revealed that a patent for an optimal solution had already been issued in 1988. See: Web Link. A trip to the website for Watts, Web Link revealed the product which resulted from that patent: Governor 80 Ball Cock and Thermal Expansion Relief Valves are triple-function devices: a toilet tank ball cock, an anti-siphon backflow preventer and a thermal expansion pressure relief valve. Local plumbers, and plumbing supply companies were not aware of it’s existence. I contacted the manufacturer to apprise them of the situation. They sent me a complimentary unit which I installed in one of my friend’s toilet tanks in 10 minutes. Subsequently, pressure peaks following hot water use have been limited to 120psi.

Additional information about thermal expansion can be found at:

Web Link

It is unlikely that this is an isolated incident. Homeowners who have noticed an initial burst of water when they turn on a faucet should have their system checked. It would behoove the plumbing industry to educate their operatives on the hazards of thermal expansion in home water heater systems, and the available solutions. And, an outreach program targeting communities where this problem is likely to exist should be undertaken.