Before a sewer line backup necessitates an expensive repair, check if your homeowner's insurance policy covers sewer pipe repair or replacement.

Most policies exclude repairs needed due to damage caused by gradual wear and tear, a fact that surprises many homeowners, says Amy Bach, executive director of United Policyholders, a consumer advocacy group.

"They think a sewer backup is sudden and accidental," she says. "They think: 'Yesterday, my toilet was flushing and today things are coming out of it and it's not cool!'"

However, Bach says if you shop around or consult an independent insurance broker, you may find some policies that do cover it. You can also consider purchasing an added sewer and drain endorsement to your policy, which averages about $20 per year and can cover losses related to sewage backup, such as carpet or other damage.

Some utility companies also offer protection plans for various home systems, including sewer pipes, through companies like HomeServe USA. HomeServe partners with utility companies in 36 states, including California, Arizona and Pennsylvania.

The firm's plans, which run about $9 to $10 per month, will cover sewer line repairs up to about $3,000 to $5,000 per service call, says senior vice president Myles Meehan.

HomeServe's network of contractors, who are on call 24 hours a day, make the repairs. Bach of United Policyholders cautions any consumer who is considering these programs to make sure they understand what's excluded in the policy before relying on it to cover their costs.