Thermal Expansion

ATTENTION:       Sunriver Water customers who have a Backflow Prevention Assembly on the water service line to your home or place of business.

All customers who have a Backflow Prevention Assembly on the water service line to your home or place of business need to be aware of thermal expansion.

Water heaters are installed with a temperature and pressure valve (T & P) which is designed to relieve excessive water temperature or pressure.  Also aiding in the control of excessive heat and pressure is a condition known as thermal expansion which allows extremely hot water to backflow through the water meter into the water main line, mixing with the cold water and dissipating the heat.

However, when a backflow prevention assembly is installed on a water service line the water cannot go back out into the water system.  This leaves the T & P valve as the only release route for the overheated water.  If the water heater thermostat becomes defective allowing the water temperature to increase to more than 212 degrees and the T & P valve fails, the water can become “superheated”.  Superheated water can cause water heaters to explode or can allow scalding steam to be released from the faucets upon personal use.

This condition is rare, because the water heater thermostat and the T & P valve must both malfunction simultaneously.  However, with the backflow prevention assembly in place, the potential hazard exists.

Sunriver Water LLC recommends that the T& P valve be inspected periodically.  A licensed plumber can inspect, repair or replace the T & P and assist you with other methods of protection.  We highly recommend that you have a thermal expansion tank installed for added protection.

Should you have questions or desire more information, please feel free to contact our office between 7:00 a.m. to 3:00 p.m. Monday through Friday at 541-593-4197.

References:   http://public.health.oregon.gov/healthyenvironments/drinkingwater/rules/documents/61-0070.pdf

OAR CHAPTER 33

Division 061

333-061-0070 Cross Connection Control Requirements

(8) Premise isolation requirements:  (A) The water supply shall (iii) Notify the premise owner and water user, in writing, of thermal expansion concerns.

Mailing June 2012

Serving the Sunriver, Crosswater, Caldera Springs and Vandevert Ranch communities of
Central Oregon. Contact us during regular office hours Monday - Friday 7:00am - 3:00pm
at (541) 593-4197. During after hours, we can be reached at (541) 419-6469.