Why Your Washing Machine Backs Up When It Drains

During the drain cycle, a washing machine pumps a large volume of water into the plumbing system in a relatively short amount of time. If the drain line can't keep up, water may back up out of the standpipe or nearby drain instead of flowing normally into the sewer line.

This is usually caused by a clog or restriction somewhere in the plumbing system. Finding where the blockage is located is the first step toward getting the drain flowing properly again.

How a Washing Machine Drain Is Designed to Work

Most washing machines discharge into a vertical drain pipe called a standpipe. As the washer pumps water out, it flows down the standpipe, through a trap and into the home's branch drain before eventually reaching the main sewer line.

The drain system is also connected to a plumbing vent, which allows air into the piping as water moves through it. This helps air move through the system so wastewater can drain without fighting pressure inside the pipe.

When the drain line is clear and properly vented, it should have no trouble handling the volume of water released during a normal wash cycle.

Common Reasons a Washing Machine Drain Backs Up

• A partial blockage in the drain line: Soap residue, lint and other debris can gradually reduce the amount of water the pipe can carry.
• A clogged standpipe or trap: Blockages close to the washing machine may prevent water from draining as quickly as it's being discharged.
• Improper venting: If the plumbing vent isn't functioning correctly, wastewater may drain more slowly than it should.
• A blockage farther down the sewer line: If the restriction is beyond the laundry drain, the washing machine may simply be the first fixture to reveal the problem.

What Should You Do if Your Washing Machine Drain Starts Backing Up?

Stop the washing machine and do not keep running cycles to see if the drain clears on its own. Don’t pour chemical drain cleaners into the standpipe because they may not clear the blockage and can create safety issues for anyone working on the drain later.

You can clean up standing water, check whether nearby fixtures are also draining slowly and schedule a plumbing inspection to locate and clear the blockage properly.

Why It Usually Happens During the Drain Cycle

A washing machine pumps out a significant amount of water in a relatively short period of time during the drain cycle. A drain that seems to handle smaller amounts of water from sinks or bathroom fixtures may not be able to keep up once the washer begins emptying its tub.

That's why partially clogged drain lines often go unnoticed until laundry day. The plumbing system may appear to work normally most of the time, but the washing machine places enough demand on the drain to expose an existing restriction.

When the Problem Is Bigger Than the Laundry Drain

Sometimes the washing machine drain isn't the real source of the problem.

If you also notice slow drains elsewhere in the house, toilets that gurgle, showers backing up or wastewater appearing in another fixture when the washing machine drains, the blockage may be in the home's main sewer line rather than the laundry branch drain.

A sewer line problem can affect multiple plumbing fixtures throughout the home, even if the washing machine is the first place you notice symptoms. Having the drain system inspected can determine whether the issue is isolated to the laundry drain or involves the main sewer line.

Our Arlington Plumbers Can Restore Proper Drainage to Your Laundry Room

A washing machine drain that backs up every time it empties is unlikely to fix itself. Our plumbers at Tom's Mechanical can inspect your plumbing system, identify whether the backup is caused by the standpipe, branch drain or main sewer line, and recommend the appropriate repair.

Call us at 817-277-4493 and we’ll dispatch a plumber to diagnose the issue and get your drain flowing properly again.