You will get error code F21 on your Whirlpool Duet washer when the unit is taking too long to drain. Being a drainage problem, you need to inspect the drain hose for kinks or clogs that may be locking the flow of water. You may also get this error when you use the wrong detergent on the front load washer. 

You may also get this error code on your washer when the drain pump is not working or the drain pump filter is clogged. However, it may also be triggered by a minor glitch on the circuit board of the washer. As such, it is advisable to first reset the Whirlpool front load washer to clear the error code.

If the error resurfaces after your have reset the machine, you can use the methods discussed in this guide to troubleshoot and fix it. 

In proper working condition, the Whirlpool Duet washer should drain in less than 8 minutes. If it takes longer than that, the Whirlpool Duet washer error code F21 will be triggered. In most cases, the error code man’s that something is blocking the normal flow of water down the drain hose. 

To fix the problem, you should first reset the washer to clear the error. If it reappears after resetting, you need to check the drain hose, and filter for clogs and remove them. Using the wrong detergent on the washer can also trigger error code F21 due to excessive formation of suds. 

Be sure to use the recommended high-efficiency (HE) detergent only. If none of these is the problem, you should have the drain pump diagnosed and replaced, if faulty. 

What Causes the Whirlpool Duet Washer Error Code 21? 

Washing machine error code, including error code F21, are often triggered by a glitch within the Whirlpool washer circuit board. In such a case, resetting the machine will clear the error code form display. Error code F21 can also point to a problem within the drain system. 

Here are some of the things that are known to trigger the Whirlpool washer error code F21:

Improper Installation 

If the washer was recently installed or moved, the problem is more likely to be Improper Installation. As you are aware, different requirements need to be met while choosing the location and installing the washing machine. If the drain hose was not installed properly, it could hinder drainage from the washer. 

For instance, installing the drain hose higher than 96″ from the floor can lead to siphoning. This hinders smooth flow of water from the machine, hence triggering error code F21.

Drain Hose Blockage 

Due to accumulation of lint along the drain hose and on the drain pump filter, you should expect the drain system to clog occasionally. This is actually the leading cause of the Whirlpool Duet washer error code F21. To restore it to it’s working condition, you need to clear the clog(s) and clean the drain system. 

In cold weather, water may freeze in the drain hose, hindering the flow of water. It is also possible for kinks to develop along the drain hose due to vibrations. This can also trigger the F21 error code. 

Clogged Drain Pump Filter

The drain pump filter is installed along the drainage system to filter dirt and debris, especially flint, so that it does not get into the pump. Accumulation of flint, forth and debris on this filter—which is normal—will naturally slow the flow of drain water or block it altogether. 

This will, in turn, trigger error code F21 on your Whirlpool Duet washer. In this case, you need to remove the filter and clean it thoroughly to allow for free flow of drain water. 

Drain Pump Issues 

Whirlpool Washer drain pumps are designed to offer extended durability. Before you rush to replace yours, first check its wiring for damage or loose connection. Inspect the wire harness and wiring connecting the pump to other components, such as the central control unit (CCU) and the pressure switch. 

Next, you should diagnose the pressure switch itself as a malfunction can also trigger error code F21. If none of these seem to be the problem, you can have the whirlpool washer drain pump diagnosed and replaced, if need be. 

Using the Wrong Detergent 

Almost all the Whirlpool front load washer models require you to use high-efficiency (HE) detergents. Using the wrong type of detergent on the machine may result in excessive suds formation during the wash cycle. 

The excess suds will then accumulate on the drain system and slow, or stop the flow of drain water. Using too much detergent will also have a similar effect. For instance, the concentrated detergents labeled 2x and higher only require a small amount of detergent—depending on the current load size. 

If you happen to have used the wrong or excess detergent on your Whirlpool Duet washer, just empty the washer, run a Rinse/ Spin cycle, and then run the Normal cycle without any detergent. This will clear the system of the excess detergent and suds that may have formed as a result. 

How to Fix the Whirlpool Duet Washer F21 Error Code 

As mentioned earlier in this guide, the F21 error code on Whirlpool Duet washers may be triggered by a glitch on the Central Control Unit (CCU). This can happen even when the drain system is working as it should. To rule this cause out, you need to clear the error code from the display. 

Here is how you can clear the Whirlpool Duet washer error code F21:

Step 1: Start the Duet washer then press the Pause/ Cancel button. In some Whirlpool washer models, you may need to press the Pause/ Cancel button twice to clear the error from the display. 

If this does not clear error F21 from the display, proceed to the following steps to hard reset the Whirlpool Duet washer. 

Step 2: Turn the washer off, disconnect its power cord from the outlet socket, and let it sit unplugged for about 15 minutes. This allows the capacitors to drain any charge they may be holding this resetting the machine. 

Step 3: Plug the washer back into the outlet socket and power it on by pressing the Start button. Having reset the machine, error code F21 should disappear from the display, at least temporarily. Now re-select the cycle and press the  Start button the control panel.

If it comes back, then it is not just a CCU glitch, but a more serious issue that needs to be addressed right away. In such a case, here are some of the methods and steps you can use diagnose and fix Whirlpool Duet error code F21: 

Method 1: Check Whether the Drain Hose is Installed Properly 

If you are getting error F21 on a washer that was recently installed or moved, the problem could be poor installation of the drain hose. If you took time to read the user manual that come with your Whirlpool Duet washer, you should have seen the installation requirements. 

If the drain hose on your washer does not meet the minimum requirements, as stipulated by the user manual, it is more likely to cause drainage issues. If it happens to slow the drain water flow rate, it is likely to result in error F21 sooner or later. The drain system for your washer should be installed using a wall standpipe, floor drain, a floor standpipe, or a laundry tub. 

To avoid siphoning in either case, only 41⁄2″ of the drain hose should be in the standpipe, and should be secured properly using cable ties. You can use whichever drain system that suits your needs, but the installation requirements for each are different, as elaborated: 

Floor Standpipe Installation Requirements 

If you choose to install a floor standpipe drain system for your Whirlpool Duet washer, the standpipe should be at least 2″ in diameter and have a minimum capacity of 17 gal per minute. The top of the standpipe needs to be between 24″ and 49″ high—from the bottom of the washer or floor. 

If you need to use an overhead sewer, whereby the drain water has to be pumped higher than 96”, you will need a sump pump, and the associated accessories for the installation. Such requirements also apply to Wall standpipe drain system installations. 

Floor Drain System Installation Requirements

 If you would rather install a floor drain system for your Whirlpool Duet washer, you need to buy the appropriate Siphon Break Kit for the installation (Sold separately). You will also need an extension drain hose for the installation (also sold separately).

The minimum siphon break for a floor drain system is 28″ from the bottom of the washer. 

Laundry Tub Drain System Installation Requirements 

If you are installing a laundry tub drain system for your Whirlpool Duet washer, it should support a flow rate of at least 20 gal per minute. The top of the laundry tub should be between 24″ and 49″ from the floor.

Check the Drain Hose for Kinks 

As the machine vibrates during use, it is possible for the drain hose to bend and develop kinks. These will, in turn, slow the flow of drain water through the hose. To avoid such a scenario with your washer, it is advisable to install a U-shaped drain hose and secure it properly. 

Located behind the washer, examine the drain hose for any bends or kinks throughout its length. If found, you need to straighten them to allow for free flow of drain water, and possibly clear error code F21. You may use a rigid plastic frame to accomplish this.

Method 2: Unclog the Drain Hose 

 Next, you need to examine the drain hose for clogs that may be preventing the water from flowing. To unclog the Whirlpool Duet washer drain hose, these are the steps you should take:

Step 1: Shut the washer down and unplug it from the power source. 

Step 2: Move the washer away from the walls to allow for easy access to its back. You should then disconnect the hose and inspect it for clogs. Having disconnected the hose from the washer, you should unclip it from the cable ties to remove it. 

Step 3: Now blow into the hose or run water through it under pressure to diagnose, and possibly clear clogs. If the water cannot go through, you need to reach into the hose with a long-handled hook and pull out the flint out. You may also use a flexible wire to push the clog out of the hose. 

Having removed the dirt and pieces that were blocking the hose, you should run water though the hose to clean it. 

Step 4: Once you are done, reconnect the hose to your washer—as directed in the user’s manual—and secure it in place using the cable ties. 

Method 3: Clean the Drain Pump Filter

If the drain hose was not clogged, the blockage is probably at the filter. In this case, you should remove the filter and clean it. Just unplug the washer and move it to an open location. To access the lower panel, tilt the washer back, and place several 2 x4 pieces under the long side to keep the unit tilted. 

Next, remove the three 1/4′ screws holding the bottom panel in place then pull the white panel down. This should expose a white circular filter that features a turning handle. This is the filter you need to remove and clean. Position a shallow container below the filter to collect the drain water. 

Now twist the filter handle, remove all the dirt and debris that had been collected behind the filter, and then clean the filter thoroughly. Once done, re-insert the filter, close the panel and start the washer. Run a test cycle to check whether error F21 has been fixed. 

Method 4: Check the Drain Pump for Clogs 

Even with a working filter in place, it is still possible for the drain pump to get clogged. In most cases, this occurs inside the corrugates tubes leading to and from the pump. Having unplugged the washer from the outlet socket, follow the steps explained in method 2 above to remove the bottom panel. 

You will find the pump at the bottom of the machine, right behind the front bar. Once you locate the drain pump, remove the drain pump filter and any dirt that it may be holding. Next, run pick into the corrugated tubes to remove any foreign object that may be lodged into the tubes. 

Now run some water under pressure through the pump to clear it of any flint that may be hindering water from flowing. Once done, reassemble the parts back together, plug the machine back in and run a test cycle to see whether error code F21 resurfaces. 

Method 5: Only Use HE Detergent 

As mentioned earlier in this guide, using the wrong or excess detergent on your wash cycles will lead to formation of excessive soap suds. The suds may collect in the drain system with time, and slow the flow of water down the hose. 

Being an energy-efficient washer model, the Whirlpool Duet requires you to use high-efficiency detergents. If you suspect suds to be causing the Whirlpool Duet washer error code F21, start the washer and select the ‘Drain/Spin’ cycle. 

Thereafter, you should only use detergents labeled HE on your washer. Check the label on the detergent container for the right amount to use per wash cycle. This is the amount you should fill into the dispenser before the cycle, depending on the load size. 

Final Verdict 

Error F21 on a Whirlpool washer is a low drain error to tell you that the machine is taking too long to drain. If the machine fails to drain in 8 minutes, the cycle is automatically terminated and error code F21 displayed on the control panel. 

The inability to drain in time is often caused by a clog in the drain system—in the drain hose, filter or drain pump. Using the wrong detergent can lead to the formation of excess suds, which slow the drainage process. Regardless of the cause, this guide will help you troubleshoot and fix the Whirlpool Duet washer error code F21.