⚠ What This Means
The display shows -20 with the corresponding zone indicator flashing. This means the zone thermistor in that zone is unplugged or has an open circuit. The unit cannot read the temperature in that zone.
Caution: The unit must be power-cycled (OFF 10 seconds, then ON) after thermistor replacement to clear the error. Simply reconnecting the thermistor will not clear the display.
🔧 How to Fix
- Identify which zone indicator is flashing to determine the affected thermistor.
- Check the wiring connections to the zone thermistor — reconnect if unplugged.
- Test thermistor resistance: should read approximately
32,500 ohms at 32°F and 10,000 ohms at 77°F. - If resistance is out of range or open, replace the thermistor.
- After repair, turn the unit OFF at the master power switch for 10 seconds.
- Turn the unit back ON to clear the error mode.
Test Specifications
Thermistor at 32°F (0°C): ~32,500 ohms
Thermistor at 77°F (25°C): ~10,000 ohms
🛒 Replacement Parts for This Fix
Zone Thermistor
~32,500 ohms at 32°F
Digital Multimeter
For resistance testing
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❓ Frequently Asked Questions
What does -20 mean on my Sub-Zero 700?
Error -20 means the zone thermistor is disconnected or has failed open. The flashing zone indicator shows which zone is affected.
How do I test a Sub-Zero 700 thermistor?
Measure resistance with a multimeter. At 32°F it should read approximately 32,500 ohms. At 77°F it should read approximately 10,000 ohms.