The F35 / Sud error code is one of the more common codes to pop up in the display of the late-model Whirlpool Duet front load washers. There's a lot of urban mythology out there on the Internet about these codes, their causes, and how to fix them. I'm going to deal with the two most prevalent myths out there and inoculate you against their error.
Urban Myth Number 1: "The F35 / Sud error code is caused by a clogged drain pump and to fix it, you have to clean out the drain pump cleanout port."
Reality: The drain pump and its cleanout port have absolutely nothing to do with this particular error code. The control board is programmed to display completely different error codes pertaining to the drain pump such as:
- F01 Pump driver error
- F21 Long drain time
- F27 Overflow condition
You can find these yourself on the tech sheet located inside the washer, either under the top panel or behind the bottom front panel. On that tech sheet, you'll see over six pages of very specific error codes-- 30 in all! -- dealing with distinct, specific aspects on the machine's function and operation.
The F35 error code specifically deals with faults related to the Analog Pressure Sensor (APS). The Sud error code pertains to excess suds detection in the machine. When these two codes occur together (and they don't always), it leads you to a very specific diagnosis but one which has nothing to do with the drain pump.
I know there's a video out on Youtube with a lot of views where the guy claims this fixed it but I assure you that was purely coincidental. He was a DIYer who was just guessing. Saying that a poor drain caused the F35 / Sud error combo is like saying a flat tire caused your car engine to quit starting.
Urban Myth Number 2: "To clear the F35 error code, try pulling the rubber tube off the APS and blowing hard into the tube nipple on the APS to reset it."
Reality: Blowing into the APS does absolutely nothing good. But it does ruin an APS that was already good. These are not like the old bellows pressure switches. Analog pressure sensors are digital transducers that convert an analog pressure into a digital information stream for the CCU. Telling people to blow into the APS is simply going to make them ruin a hundred+ dollar part.
There is some merit, however, to pulling the black rubber tube off the APS and blowing into it back toward the drum (NOT into the APS) to clear any gookus that may have gotten lodged in there and is interfering with the changes in air pressure being sent up the tube to the APS.
The Light of Truth
Let's take a walk through a Whirlpool Duet washer with the F35 / Sud error code combo and investigate its real cause and how to fix it:
Here's the link to the Analog Pressure Sensor (APS) that I replaced to fix the problem in this particular model: http://www.repairclinic.com/PartDetail/Pressure-Switch/W10415587/1938628
As mentioned in the video, a defective APS is the single-most common cause for the F35 / Sud error code combo. There are at least two variations on the APS theme, so be sure to look up the correct sensor based on your complete model number and buy it here. That way, in the off chance that the APS doesn't fix it, you can return it for a refund and buy either the CCU or the Steamer board.