Whirlpool Dishwasher Error Code F20 — What It Means & How to Fix It

What Does This Error Mean?

Whirlpool dishwasher error F20 means the water softener salt sensor has detected a problem — either the salt level is too low or the sensor itself has a fault. The built-in water softener uses salt to prevent limescale buildup inside the dishwasher. In most cases, simply refilling the salt reservoir fixes F20 immediately.

Affected Models

Whirlpool WDT750SAHZ
Whirlpool WIO3O33PLE
Whirlpool WSIO3O23PEF
Whirlpool WDT970SAHZ
Whirlpool WDTA50SAHZ

Common Causes

The salt reservoir is empty or nearly empty and needs to be refilled with dishwasher salt
Tap water has been used instead of dedicated dishwasher salt, or table salt has been used, which can clog the salt sensor
The salt sensor is coated with a mineral deposit from hard water and is giving a false low reading
The cap on the salt reservoir is not sealed correctly, allowing water to dilute the salt too quickly
The water softener sensor has failed and needs to be replaced

How to Fix It

Open the dishwasher door and pull out the lower rack. The salt reservoir cap is on the floor of the dishwasher tub, usually on the left side — it has a round cap you unscrew.

Place a towel on the floor under the dishwasher — a small amount of water may spill when you unscrew the cap.
Unscrew the salt cap and check the level inside. If it is empty or low, fill it with dedicated dishwasher salt — not table salt or water softener granules. Fill it right to the top.

Only use coarse-grain dishwasher salt (sold in supermarkets near dishwasher tablets). Table salt contains additives that can damage the water softener unit.
Replace the salt cap and screw it on firmly. Run a rinse cycle to circulate the new salt through the system before running a full wash.

The F20 error may take one full cycle to clear after refilling the salt. This is normal.
If the error persists after refilling, clean the area around the salt sensor. Use a soft damp cloth to wipe inside the salt reservoir opening and remove any salt crust or mineral deposits around the sensor.

A white crusty buildup around the sensor is common in hard water areas and can cause false readings.
If F20 continues even with a full salt reservoir and a clean sensor, the salt sensor has likely failed. A technician can confirm this and replace the sensor — it is a relatively affordable repair.

Salt sensor faults are uncommon but do occur in older dishwashers or those that have used the wrong type of salt for extended periods.

When to Call a Professional

If refilling the salt reservoir and cleaning the sensor does not clear F20, the sensor or the water softener unit may need professional replacement. Contact a Whirlpool-certified technician if the error persists after completing all the steps below.

Frequently Asked Questions

What type of salt should I use in my Whirlpool dishwasher?

Always use coarse-grain dishwasher salt specifically made for dishwashers. Do not use table salt, sea salt, or water softener pellets — these contain additives that can damage the water softener unit and clog the salt sensor. Dishwasher salt is inexpensive and widely available in supermarkets.

How often should I refill dishwasher salt?

How often you need to refill depends on your water hardness and how often you run the dishwasher. In hard water areas, you may need to refill every 4–6 weeks. In soft water areas, every few months is common. Most Whirlpool dishwashers have a salt indicator light — watch for it to come on.

Do I need dishwasher salt if I use all-in-one tablets?

In soft water areas, all-in-one tablets with built-in softener may be sufficient. In hard water areas, the built-in softener in all-in-one tablets is usually not enough — you still need to use the salt reservoir. If you live in a hard water area and skip salt, you will see limescale buildup inside the machine over time.