Seattle, Wash. - CenturyLink said Monday 4,500 911 calls did not go through during an unprecedented six-hour statewide outage last week.
The company said the outage was not caused by failures of CenturyLink's network and was unrelated to any OpenSSL problems such as the Heartbleed bug.
A company statement blamed a "technical error in a third-party vendor's call router, which prevented the system from properly processing calls."
The statement did not name the vendor.
CenturyLink works with Colorado company Intrado to provide 911 service. Intrado sent KIRO 7 a statement saying the outage "was caused by an isolated system issue that was promptly resolved after root cause identification."
The statement did not identify the issue, nor explain what made it isolated.
911 centers across Washington first noticed a problem in the early hours of April 10.
CenturyLink says in addition to the 4,500 911 calls that did not go through, 770 calls did connect between 12:36 a.m. and 6:26 a.m. when service was restored.
During the outage, a woman in Everett said she tried 37 times to call 911 when an intruder entered her home. She eventually reached police on another number and was unhurt.
In a statement, CenturyLink Northwest Region President Brian Stading said, "Our 911 system has been returned to normal operations and we are confident these steps have addressed this issue."