The short answer
F21 means the cooktop has found a problem with the frequency of its power supply: the electricity arriving does not alternate at the rate its electronics expect. On normal grid power that is unusual and often passes; on a generator or inverter it is a common cause, and the cooktop should not be used until the supply is right.
Error codes
Reference| Code | Meaning |
|---|---|
| F21 | There is a problem with power supply frequency. |
What the cooktop does with the code showing
- The code appears while the house runs on a generator — Generators can drift off the expected frequency, especially under load.
- It appeared during a storm or utility disturbance — Grid disturbances are brief and usually clear.
- Other electronics or clocks misbehave too — A supply problem affects more than the cooktop.
- NEAR MISS: the cooktop is completely dead — That is no supply at all; check the breaker first.
Likely causes, in order
- Backup generator or off-grid inverter — The most common cause: a supply that is not utility power, or a generator under heavy load, drifts off the expected frequency.
- Utility supply disturbance — Second: a brief grid problem, which passes and clears after a reset.
- Power board sensing fault — Third: on steady, normal grid power, a code that returns points at the cooktop’s power electronics.
Where to start, and what comes next
- Confirm what the house is running on — Generator, inverter or utility power.
- Wait for steady grid power and reset — Breaker off for a minute once the supply is normal.
- Check other sensitive electronics — Misbehaving clocks or electronics confirm a supply issue.
- Technician checks the power board — Only if the code returns on normal grid power.
What you can safely do
- Supply check — Note whether the house is on generator or inverter power, or on the utility supply.
About 2 min
- Breaker reset on normal power — Once utility power is steady, switch the cooktop’s breaker off for a minute, then on.
About 2 min
- Generator load check — If you must cook on generator power, reduce other loads; a heavily loaded generator drifts the most.
About 5 min
- STOP here if the next check needs a panel off — Anything behind a panel is a power-off technician job, and the tests that follow it are made on live circuits.
Power off before any panel
Safety
Switch off the cooktop’s breaker before removing it from the counter or opening anything underneath: most cooktops are hard-wired, with no plug to pull. A capacitor can hold a charge after the power is off. Let the glass cool before cleaning or inspecting it.
The point to call
Call only when F21 returns on steady utility power after a breaker reset. On generator or inverter power the fix is the supply, and an electrician or the generator supplier is the right call, not an appliance technician.
Neighbouring codes
Scope of this reading
The reading above covers Amana electric and induction cooktops with touch controls. It does not cover Amana gas cooktops, Amana ranges, whose surface codes are listed with the oven codes, or sister brands on the same platform, whose lists can read differently. A model-specific page for F21, where one exists, is the more specific answer; none exists yet, so check the use-and-care guide for your exact model before ordering any part.
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Lead Appliance Repair Technician · 12 years experience
Experienced technician with 12 years specializing in washing machine and dryer repairs across all major brands.
