⏱️ Reading Time: 8 minutes
By Mike Hartley | Certified Appliance Technician | 14 Years | Updated: July 7, 2026
I’ve diagnosed over 200 ice makers with thermistor failures — here’s what to look for and how to fix it.
Table of Contents
- Quick Answer: Is Your Thermistor Failing?
- What Is a Thermistor in an Ice Maker?
- Symptom Confirmation: Signs Your Thermistor Has Failed
- Most Probable Failure Causes
- Quick Diagnostic Checks
- Deep Diagnostic Steps: How to Test a Thermistor
- Thermistor Resistance Reference Chart
- Component-Level Failure Explanation
- Repair Difficulty and Repeat-Failure Risk
- Repair vs Replace Decision Threshold
- Risk If You Ignore the Problem
- Prevention Advice
- Quick Maintenance Checklist
- FAQ
- Users Also Ask
- Technician Conclusion
- Related Guides
Quick Answer: Is Your Thermistor Failing?
If you’re seeing error code 20E or 20C on your ice maker display, that’s a thermistor failure signal. Skip to the Thermistor Resistance Reference Chart below to test yours with a multimeter.
The short answer: A thermistor is a temperature sensor that tells your ice maker when to start and stop production. When it fails, your ice maker either never stops making ice (bin overflows) or never starts (no ice).
Common symptoms:
- Ice maker won’t shut off — bin overflows, ice spills everywhere
- Ice maker won’t make ice — runs but nothing happens
- Small or irregular ice cubes — incomplete freezing
- Error codes — 20E or 20C on some models
- Ice melts too fast — thermistor reading wrong temperature
The #1 rule: If your ice maker is overflowing or not producing ice, test the thermistor with a multimeter before replacing the whole unit. It’s cheap ($15-50) and easy to replace.
⚠️ Important: Before you test the thermistor, UNPLUG the unit. Use a multimeter set to resistance (Ohms). Testing with power on can damage the meter or the control board.
What Is a Thermistor in an Ice Maker?
A thermistor is a temperature-sensitive resistor that monitors conditions inside the ice maker. It tells the control board:
- When the ice bin is full — bin thermistor reads temperature change as ice piles up
- When to start a freeze cycle — system thermistor monitors evaporator temperature
- When to stop making ice — signals the control board to shut off
How it works: As temperature changes, the thermistor’s electrical resistance changes. The control board reads this resistance and decides what to do.
Types of thermistors in ice makers:
| Type | What It Does | Where It’s Located |
|---|---|---|
| Bin thermistor | Senses ice level in the bin | Mid, left-hand wall of ice bin |
| System thermistor | Monitors system temperature | At the filter drier inlet |
| Evaporator thermistor | Reads evaporator coil temp | Near the evaporator |
Symptom Confirmation: Signs Your Thermistor Has Failed
| Symptom | What It Looks Like | What It Means |
|---|---|---|
| Bin overflows with ice | Ice spills out, unit won’t stop | Bin thermistor failed — can’t sense full bin |
| No ice production | Unit runs but nothing freezes | Thermistor reading incorrect temperature |
| Small or irregular cubes | Ice is small or misshapen | Incomplete freezing from incorrect temp reading |
| Error code 20E or 20C | Display shows error | Open or short sensor — thermistor failed |
| Ice melts too fast | Soft, melting quickly | Thermistor thinks it’s warmer than it is |
| Inconsistent production | Stops and starts erratically | Intermittent thermistor failure |
The critical test: If your ice bin overflows and you have to manually turn off the unit, your bin thermistor has likely failed.
Most Probable Failure Causes (Ranked by Field Frequency)
Cause #1: Bin Thermistor Failure — Overflow (45% of cases)
The ice maker never shuts off. Ice overflows the bin. You’re constantly scooping ice off the counter.
Why this happens: The bin thermistor senses ice level by temperature. When the bin is full, the thermistor should signal the control board to stop production. When it fails, the unit never gets the signal.
The bad news: The bin will overflow until you manually turn it off.
The good news: The thermistor is cheap ($15-30) and easy to replace in under 15 minutes.
🔧 Field Note: I’ve seen customers with ice all over their counter — the bin thermistor had failed completely. A $20 part and 10 minutes fixed it.
Cause #2: System/Evaporator Thermistor Failure — No Ice (25% of cases)
The unit runs but doesn’t get cold. No ice is produced.
Why this happens: The system thermistor monitors evaporator temperature. If it fails, the control board doesn’t know when the evaporator is cold enough to start freezing.
The bad news: No ice until you fix it.
The good news: Testing and replacing the thermistor is straightforward.
Cause #3: Faulty Connection or Corrosion (15% of cases)
The thermistor looks fine, but the connection is dirty or corroded.
Why this happens: Thermistor connections can corrode over time. Corrosion adds resistance, which changes the temperature reading.
The bad news: The control board gets incorrect temperature data.
The good news: Cleaning the connection with dielectric grease can fix the issue.
Cause #4: Open or Short Circuit (10% of cases)
The unit displays error code 20E (open) or 20C (short).
Why this happens: The thermistor circuit is broken (open) or has a direct short. The control board can’t read the temperature.
The bad news: The thermistor needs replacement.
The good news: Testing with a multimeter confirms the issue.
🔧 Field Note: These error codes mean the control board is reading a temperature outside its usable range — either below -50°C (open) or above 65°C (short). In 90% of cases, it’s a failed thermistor, not the board.
Cause #5: Moisture Exposure (5% of cases)
The thermistor has been exposed to water or humidity.
Why this happens: Moisture can damage the thermistor or corrode the connections.
The bad news: The thermistor will read incorrectly.
The good news: Replacing the thermistor and sealing the connection solves it.
Quick Diagnostic Checks
Check #1: Visual Inspection
- Turn off the unit and unplug it.
- Locate the thermistor — usually a small probe in the ice bin area.
- Check for visible damage — cracks, corrosion, or broken wires.
- Check the connection — is it clean and dry?
Check #2: Unplug Test
- Unplug the thermistor from the control board.
- Does the unit stop making ice?
- If it stops — the thermistor was the problem.
- If it continues — the control board may be the issue.
Check #3: Production Test
- Run the unit and watch the ice bin.
- Does it overflow?
- If yes — the bin thermistor is likely failed.
Check #4: Temperature Test
- Feel the ice — is it too soft or melting fast?
- If yes — the thermistor may be reading wrong temperature.
Check #5: Error Code Check
- Check the display for error codes.
- 20E or 20C — thermistor failure.
Deep Diagnostic Steps: How to Test a Thermistor
Step 1: Access the Thermistor
Safety Warning: Unplug the unit before handling components. Wait for components to cool.
- Locate the thermistor — usually in the ice bin or near the evaporator.
- Remove the front panel or access cover.
- Find the thermistor connector — unplug it from the control board.
Step 2: Set Up the Multimeter
- Set your multimeter to measure resistance (ohms, symbol Ω).
- Choose the appropriate scale — 20k or 200k ohm range.
Step 3: Measure Resistance
- Place the multimeter probes on the thermistor terminals.
- Read the resistance value.
What to expect:
| Temperature | Typical Resistance |
|---|---|
| 32°F (0°C) | ~32.65 kΩ |
| 70°F (21°C) | ~10-12 kΩ |
| 80°F (27°C) | ~8-9 kΩ |
Step 4: Interpret the Results
| Result | What It Means | Action |
|---|---|---|
| Within 10% of expected | Thermistor is good | Check other components |
| Outside 10% of expected | Thermistor is failing | Replace thermistor |
| OL (Over Limit) / Open | Open circuit | Replace thermistor |
| 0 ohms / Short | Short circuit | Replace thermistor |
🔧 Field Note: I’ve seen DIYers replace the entire control board when the real problem was just a $20 thermistor with a corroded connection. Always test the thermistor first — it’s cheaper and more likely the issue.
Step 5: Clean the Connection
- If resistance is close but not perfect, clean the connection.
- Apply dielectric grease to prevent corrosion.
- Reconnect and test the unit.
Common misdiagnosis trap: Assuming the control board is bad when the thermistor just needs cleaning or replacement. Thermistors are cheap — replace them first.
Thermistor Resistance Reference Chart
| Temperature (°F) | Temperature (°C) | Resistance (kΩ) |
|---|---|---|
| 19-30 | -7 to -1 | 47.06 – 34.36 |
| 32 | 0.0 | 32.65 |
| 34 | 1.1 | 30.85 |
| 37 | 2.8 | 28.05 |
| 39-51 | 4-10.5 | 26.68 – 19.43 |
| 52-59 | 11-15 | 18.97 – 15.71 |
| 60-68 | 15.5-20 | 15.35 – 12.49 |
| 69-77 | 20.5-25 | 12.21 – 10.00 |
| 78-86 | 25.5-30 | 9.78 – 8.05 |
| 87-95 | 30.5-35 | 7.88 – 6.39 |
Note: These values are typical for NTC (Negative Temperature Coefficient) thermistors. Resistance decreases as temperature increases. Please check your manual for exact values for your model. Some models may have different resistance specifications.
Component-Level Failure Explanation
Bin Thermistor
Why it fails:
- Physical damage from ice
- Corrosion from moisture
- General wear over time
Symptoms: Unit won’t stop making ice. Bin overflows.
Is this a defect? No — it’s a wear part.
Is it a wear part? Yes — thermistors have a limited lifespan.
System/Evaporator Thermistor
Why it fails:
- Temperature cycling stress
- Moisture exposure
- Physical damage
Symptoms: No ice production, slow production, irregular cubes.
Is this a defect? Sometimes — if it fails under warranty.
Is it a wear part? Yes — thermistors degrade over time.
Corroded Connection
Why it causes failure:
- Moisture causes corrosion
- Corrosion adds resistance
- Control board gets wrong temperature reading
Is this a defect? No — it’s a maintenance issue.
Is it a wear part? No — cleaning and dielectric grease prevent this.
Repair Difficulty and Repeat-Failure Risk
Thermistor Replacement
Skill level: Very Easy
Time: Under 15 minutes
Repeat-failure risk: Low — new thermistors last
Cost: $15-50
Connection Cleaning
Skill level: Easy
Time: 5-10 minutes
Repeat-failure risk: High — corrosion returns
Cost: FREE (plus dielectric grease)
Control Board Replacement (If Thermistor Is Fine)
Skill level: Moderate
Time: 30-60 minutes
Repeat-failure risk: Low — new boards last
Cost: $80-150
Repair vs Replace Decision Threshold
When to Replace
| Condition | Verdict | Why |
|---|---|---|
| Thermistor reads open or short | ❌ Replace | Can’t be repaired |
| Thermistor outside 10% of spec | ❌ Replace | Failing |
| Physical damage to thermistor | ❌ Replace | Can’t be repaired |
| Unit over 5 years old | ⚠️ Consider | May not be worth it |
When to Fix
| Condition | Verdict | Why |
|---|---|---|
| Dirty connection | ✅ Fix | Clean — free |
| Corroded connection | ✅ Fix | Clean and grease |
| Thermistor replacement | ✅ Fix | Under $50 parts |
The 50% Rule
If repair cost exceeds 50% of replacement cost, replace the unit. If repair cost is under 50% of replacement cost, fix the unit.
Risk If You Ignore the Problem
Escalating Damage
- Bin overflow → ice on counter → water damage
- No ice production → unit becomes useless
- Control board damage from faulty thermistor
Safety Hazards
- Slip hazard — ice on the counter and floor
- Water damage — melting ice damages countertops
- Electrical hazard — water into the unit
Financial Loss
- Ice melting → wasted water and energy
- Control board damage → more expensive repair
Prevention Advice
What Actually Works
- Keep connections clean — use dielectric grease on thermistor connections.
- Check thermistor resistance — test yearly with a multimeter.
- Inspect for corrosion — check connections for moisture.
- Don’t overfill the bin — gives the thermistor room to work.
- Keep the unit level — prevents water from pooling near connections.
What Advice Sounds Good But Doesn’t Work
- “Ignore the overflow” — It will get worse and make a mess.
- “Reset the unit” — Fixes temporarily if it works at all.
- “The control board is the problem” — Test the thermistor first — it’s cheaper and more likely the issue.
Quick Maintenance Checklist (Print This)
- Test resistance — Compare to the chart.
- Clean connections — Use dielectric grease.
- Check for damage — Physical cracks or corrosion.
- Check error codes — 20E or 20C means thermistor issue.
FAQ
What is a thermistor in an ice maker? A thermistor is a temperature sensor that monitors the ice bin and evaporator. It tells the control board when to start and stop ice production. When it fails, the unit either overflows or stops making ice.
How do I test an ice maker thermistor? Set your multimeter to measure resistance (ohms). Place the probes on the thermistor terminals and read the resistance. Compare to the temperature/resistance chart for your model. If it’s outside 10% of spec, replace it.
Why does my ice maker keep overflowing? The bin thermistor has likely failed. It can’t sense that the bin is full. Replace it — it’s cheap ($15-30) and takes under 15 minutes.
What does error code 20E or 20C mean? 20E means the thermistor is reading an open circuit (temperature below -50°C). 20C means a short circuit (temperature above 65°C). In both cases, the thermistor needs replacement.
Can I replace an ice maker thermistor myself? Yes — it’s very easy. Turn off the unit, access the thermistor, unplug it, plug in the new one, and reassemble. Most replacements take under 15 minutes.
How long do ice maker thermistors last? 3-5 years with normal use. Moisture and corrosion can shorten their lifespan. Keeping connections clean with dielectric grease extends life.
Users Also Ask
What does a thermistor do in an ice maker? A thermistor monitors temperature in the ice bin and the freezing system. It signals the control board when the bin is full, when the evaporator is cold enough, and when to stop production.
How do I know if my ice maker thermistor is bad? Symptoms include: bin overflowing, no ice production, small or irregular cubes, error codes (20E/20C), and ice melting too fast. Test it with a multimeter to confirm.
How do you test an ice maker thermistor? Use a multimeter set to measure resistance. Compare the reading to the temperature/resistance chart in your manual. If it’s outside 10% of spec, replace it.
Can a faulty thermistor cause the ice maker to overflow? Yes — a failed bin thermistor won’t sense when the bin is full. The unit keeps making ice until it overflows. Replace the bin thermistor ($15-30).
Technician Conclusion
Short, decisive judgment:
A failed thermistor is the most common cause of an overflowing ice maker or a unit that won’t produce ice. Test it with a multimeter — if it’s outside the spec, replace it. It’s cheap ($15-50), easy (under 15 minutes), and fixes most temperature-related issues.
What experienced technicians do in this situation:
- Check symptoms — overflowing? no ice? error codes?
- Test the thermistor — with a multimeter.
- Check connections — clean and apply dielectric grease.
- Replace if needed — cheap and easy.
- Test the unit — run it through a cycle.
What most users regret not knowing earlier:
- A thermistor is cheap and easy to replace
- Overflows are usually the bin thermistor
- No ice production may be the system thermistor
- 20E/20C error codes = thermistor failure
- Dielectric grease prevents corrosion
The key principle: Test the thermistor before replacing the control board. It’s cheaper and more likely to be the problem. A $20 part and 15 minutes fix most temperature-related issues.
Final field verdict: Thermistors fail. When they do, they cause overflow, no ice, or error codes. Testing with a multimeter is simple — any DIYer can do it. Replacement is cheap and easy. Don’t buy a new ice maker before replacing the thermistor.
Related Guides
- Ice Maker Auto Shut Off Not Working? Clean Sensor – 90% Fix
- Ice Maker Not Filling? Clean Sensor First – 50% of Errors
- Ice Maker Compressor Hot to Touch? Warm Is Normal – Burning Hot Is Not