Excluded “Backup” or Covered “Overflow” of Plumbing on Homeowners?

Our customer is insured under an HO 00 03 05 01. His small son flushed a tennis ball down the toilet. It got stuck and caused water to back up into the bathroom, causing extensive damage to the floor, walls, and room below.

The insurer has denied payment for this loss, citing the exclusion of “water that backs up through a sewer or drain.” We don't think this is proper application of the exclusion.

California Subscriber

When a plumbing system is blocked by something and cannot adequately handle the flow of water, the resultant loss is plumbing overflow—not sewer/drain back-up. A “sewer,” according to Webster's Collegiate Dictionary (Tenth Edition), is an “artificial usu. subterranean conduit to carry off sewage.” What overflowed in this instance was water from within the plumbing system. In citing the “backup of sewer or drain” exclusion the insurer has attempted to negate a covered peril.