mypros+
Error code reference

Whirlpool Cooktop Error Code F-21

Supply power frequency error

Whirlpool codesWhirlpool cooktop codes

Supply power frequency error — failure originates from the power control board and affects all burners on that board (Type 2).

First step from the service manual

Disconnect power, then replace the power control board.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

MyPros+ Max

Get the full diagnostic procedure for F-21.

  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What F-21 means on a Whirlpool cooktop

The F-21 error code on a Whirlpool cooktop indicates a supply power frequency error detected by the power control board. This board continuously monitors the incoming AC line frequency, which should be a stable 60 Hz in North American installations. When the board detects a frequency reading that falls outside its acceptable tolerance range, it flags F-21 and disables all burners assigned to that board. Because this is classified as a Type 2 board fault, the failure is board-level rather than a single-burner or sensor issue.

The power control board is the central processing component responsible for managing burner output, safety interlocks, and input signal validation including line frequency. A corrupted internal clock circuit, a failed oscillator component on the board, or sustained power quality issues from the supply circuit can all cause the board to misread or lose track of the incoming frequency. In some cases, a severe voltage event such as a power surge or brownout can damage the board's frequency detection circuitry permanently.

Because the error originates within the power control board itself and affects all burners on that board, component-level troubleshooting of individual burners or sensors will not resolve the fault. The diagnostic procedure calls for disconnecting power to the unit before replacing the power control board. Attempting to operate the cooktop with an active F-21 fault is not recommended, as burner control is disabled and the unit will not function normally until the board is replaced.

Source: manufacturer service documentation.

Common causes of F-21

  1. 01

    Failed power control board

    Part replacement

    The frequency detection circuitry inside the power control board has failed, causing it to report an invalid line frequency reading. Since the fault originates from the board and affects all burners on it, board replacement is the required repair.

  2. 02

    Power surge or brownout damage

    Part replacement

    A voltage event such as a surge, spike, or extended brownout can permanently damage the frequency-sensing components on the power control board. Check whether the error appeared after a power disruption in the home.

  3. 03

    Unstable or poor-quality incoming power

    Wiring / connection

    Chronic power quality problems at the supply circuit, such as fluctuating frequency from a generator or heavily loaded circuit, can trigger F-21 repeatedly. Verify that the cooktop is supplied by a stable utility power source.

  4. 04

    Loose or corroded supply wiring connections

    Wiring / connection

    Poor connections at the terminal block or junction where line power meets the cooktop can cause irregular voltage and frequency signals reaching the board. Inspect all supply wiring connections for tightness and corrosion before replacing the board.

See the test procedure for each cause

Frequently asked questions about F-21

What does F-21 mean on a Whirlpool cooktop?
F-21 on a Whirlpool cooktop indicates a supply power frequency error detected by the power control board. The board monitors incoming AC line frequency and flags this code when the frequency reading falls outside the acceptable range. All burners controlled by that board are disabled when F-21 is active. The power control board must be replaced to resolve the fault.
Can I fix F-21 myself, or do I need a technician?
The repair requires disconnecting power to the cooktop and replacing the power control board. A knowledgeable DIYer comfortable working with appliance electronics can perform this repair, but working near line-voltage components carries real risk if proper precautions are not taken. If you are not confident working with high-voltage appliance components, hiring a qualified appliance technician is the safer choice.
Will resetting the cooktop clear the F-21 error?
A power reset may temporarily clear the display, but F-21 will return if the power control board's frequency detection circuitry is genuinely faulty. Because the fault originates from within the board itself, resetting the appliance does not correct the underlying hardware failure. Board replacement is the only lasting fix.
Is it safe to use my cooktop while F-21 is showing?
No. When F-21 is active, the power control board disables the burners it controls, so the cooktop will not operate normally. You should not attempt to bypass this fault or continue using the appliance until the board has been replaced and the error is cleared.
How much does it cost to repair a Whirlpool cooktop F-21 error?
Repair costs depend on the specific power control board part price and whether you hire a technician. Parts alone typically range from around $80 to $250 or more depending on the cooktop model. Adding professional labor, total repair costs often fall between $150 and $400. Getting a parts quote for your specific model before committing to the repair is recommended.

Related Whirlpool cooktop codes

All Whirlpool cooktop codes
View all 76 Whirlpool cooktop codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass