Manitowoc Ice Machine Error Code E21: T1 Temperature Sensor
E21 means the T1 thermistor on a Manitowoc Indigo ice machine read outside its valid range during prechill. Check that the machine is still making ice and note how the slabs look. Do not unplug or pull on sensor wires; call us and mention E21.
Low: the machine keeps making ice while one sensor input is lost.
- Code
- E21
- Maker
- Manitowoc
- Equipment
- Ice machines
- Applies to
- Indigo series (non-NXT) control board, Event Log (Service menu > Event Log > View ELog)
What does Manitowoc error code E21 mean?
In the Event Log of Manitowoc Indigo ice machines without the NXT display, E21 points to the T1 thermistor. During prechill, the control board reads the sensor and averages it over six seconds. If the average falls outside the valid range, the board logs E21. That usually means the sensor or its wiring has a problem, so the board loses one of its temperature inputs. The manual describes T1 as a thermistor on the discharge line. The machine may keep making ice for a while, and staff may notice nothing, because other sensors keep the cycle going. But the board is working with less information, and its protective checks are weaker until the sensor is repaired. The display text for the entry is E21. The cause can be a loose connector, damaged terminals, a sensor that slipped from its place, or a thermistor that has gone open or shorted.
Affected models and control systems
Manitowoc Indigo series cubers with the non-NXT control board (Service menu > Event Log > View ELog). T1 is one of several thermistors; E22, E23 and E24 cover T2, T3 and T4.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- Usually nothing visible yet
- Slabs that vary a little cycle to cycle
- The E21 line in the Event Log
Possible causes
Listed in Manitowoc's documentation
- A loose T1 thermistor connector on the discharge line
- Crimped or damaged terminals on the T1 wire
- A T1 sensor that has slipped from its spot on the discharge line
- A shorted or open T1 thermistor
Other likely causes — what usually sits behind error code E21 on this control. A technician confirms which one it is before any part is replaced.
- A wire that was crushed when the compressor area panel was last replaced
- Moisture around the connector from a nearby drip or wash-down
- Vibration from the compressor that has shaken a terminal loose
Safe checks before calling for service
- Check that the machine is still making ice and note how the slabs look.
- Keep the area around the compressor dry and clear.
- Do not unplug or pull on sensor wires.
- Call us and mention that the log shows E21.
How a technician diagnoses error code E21
- Read the Event Log for E21 and look for other sensor entries.
- Inspect the T1 connector, terminals and wire route.
- Confirm the sensor sits firmly on the discharge line.
- Measure thermistor resistance and compare it with the temperature chart.
- Replace the sensor only if its resistance is wrong.
- Thermistor resistance must be read with a meter against a temperature chart.
- Sensors sit on hot discharge lines near the compressor, which can burn skin.
- A good sensor with a bad connector looks the same from outside, so it takes a test to tell.
How error code E21 differs from similar codes
E21 is the T1 sensor entry; T2, T3 and T4 each have their own numbers.
Technical reference
- Document
- Indigo Series Technician's Handbook 000014794 5/17, "Event Log" p.87-91
- Maker documentation
- Manitowoc owner support
- Edition
- Part Number 000014794 5/17
- Models / control
- Indigo series (non-NXT) control board, Event Log (Service menu > Event Log > View ELog)
- Section
- Event Log: code list p. 87, Event Log Detail table pp. 88-91 (Service menu > Event Log)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Manitowoc ice machine error codes
Can I keep running the machine with E21?
Yes, generally. It keeps making ice while the board runs with one fewer temperature input.
Will E21 clear itself?
A loose connection may settle, but a damaged sensor or wire stays out of range.
Is E21 serious?
Not by itself. It weakens protection, so it is worth having a technician repair it.
Need help with Manitowoc error code E21?
A technician confirms the cause on site and gives you the price in writing before any work starts.