Last Friday we were referred by a remediation company to a two-story home in San Fernando after a 3/4-inch orange CPVC fire sprinkler pipe burst above the ceiling. We replaced the damaged section, but the pipe didn’t just develop a small leak—it had ruptured. That made me curious about why it failed in the first place.
After the repair, we checked the water pressure and measured 172 PSI at approximately 3:00 in the afternoon. Here’s something many homeowners don’t realize: city water pressure isn’t necessarily the same throughout the day. As water demand across the system changes, pressure can change with it. When we used to perform water-supply calculations for projects served by DWP, we would obtain both the high and low pressure readings for exactly this reason. The busiest periods tend to produce lower readings, while pressure can be higher during low-demand overnight hours. So seeing 172 PSI at 3 PM gave us good reason to be concerned about what this system might experience at other times of the day.
There was another factor to consider. The existing CPVC is marked 175 PSI, and portions of the fire sprinkler piping run through the attic of this two-story home, where summertime temperatures can become extremely high. The homeowner also told us this wasn’t the first similar pipe failure in the neighborhood. We recommended installing a properly selected pressure regulator on the fire sprinkler supply to help control the excessive pressure, and we’ll be returning to perform that work.
Sometimes replacing a broken pipe fixes the immediate leak. Finding out why it broke is what can keep you from fixing it again.
