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H99

Panasonic Microwave

Severity:

Source: OnlyErrorCodes.com — Every error code. One place.

Panasonic Microwave H99 Error — Magnetron

What Does This Error Mean?

H99 on a Panasonic inverter microwave means the magnetron or inverter has failed self-test. The microwave will not heat. This is a hardware fault requiring service — Panasonic inverter modules typically cost USD 150–250 to replace fitted.

Affected Models

  • Panasonic NN-SD945S
  • Panasonic NN-SN686S
  • Panasonic NN-CT55JW
  • Panasonic NN-CD58JS
  • Panasonic NN-DS59NB

Common Causes

  • Failed magnetron (microwave generator at end of life)
  • Inverter board fault (Panasonic uses inverter technology rather than transformers)
  • High-voltage diode short
  • Cooling fan failure causing magnetron over-temperature

How to Fix It

  1. Unplug for 10 minutes.

    On rare occasions, a soft H99 from a brief over-temperature event clears after a 10-minute power-off cool-down. Plug back in and test with 30 seconds on a cup of water.

  2. Listen for the cooling fan.

    When you start a cook cycle, listen for the cooling fan — it should be audible immediately. Silence indicates a failed fan, which can cause magnetron over-temperature and H99.

  3. Check ventilation around the microwave.

    Confirm the rear and side vents are clear of obstructions and dust. A dusty external grille restricts airflow and contributes to inverter or magnetron over-temperature.

  4. Book Panasonic-authorised service.

    H99 that persists indicates the inverter or magnetron needs replacement. Panasonic inverter parts are not interchangeable with transformer-style microwave parts — use Panasonic-authorised service for the correct module.

When to Call a Professional

H99 is not user-serviceable. The microwave's high-voltage capacitor holds a lethal charge even when unplugged. Only qualified technicians with discharge tools should open the case.

Frequently Asked Questions

What is the difference between H97, H98, and H99 on Panasonic microwaves?

All three relate to the inverter/magnetron module. H97 indicates a low-side inverter fault, H98 indicates a high-side inverter fault, and H99 indicates a generic inverter or magnetron failure. The fix path is similar — service replacement of the affected module.

Is it worth repairing a Panasonic microwave with H99?

For Panasonic inverter microwaves under 5 years old, repair (USD 200–300) is usually cost-effective given the higher replacement cost of new inverter models. For microwaves over 8 years old, replacement is often the better choice.