What does Manitowoc E20 (WTR Fault) mean?

E20 is the water-system fault on Manitowoc Indigo NXT and Indigo machines. The control detected an abnormal water level or flow during fill, circulation, or drain — typically the high water probe activates without the low probe being reached first, or the pump fails to circulate water evenly across the evaporator. Diagnostic order: confirm 20–80 PSI supply, clean the inlet-valve screen, clean the sump filter and water-level probes (heavy mineral scale on the probe rods is the most common root cause), then test the water pump and drain pump separately. Replace the probes if cleaning does not restore stable level readings.

How do I diagnose a Manitowoc ice machine making too-small ice cubes?

Small ice cubes on Manitowoc machines are typically caused by low water flow to the evaporator (check supply pressure, minimum 20 PSI), a partially blocked water distribution tube (remove and clean the nozzles with a soft brush), an incorrect water purge / dump setting that wastes water mid-cycle, or a failing water inlet valve that does not fully open. Verify the inlet flow rate against the service-manual specification for your model and clean any mineral scale on the distribution tube and evaporator before adjusting the water purge.

What causes a Manitowoc machine to stop making ice with no fault codes?

Manitowoc machines that stop making ice without a displayed fault code often have: high condenser temperature triggering a protective standby (clean the condenser coil and air filter), a failed harvest assist paddle preventing cube release, the bin thermostat or ice-level sensor falsely reading bin-full (clean the probes), or a water dump valve that will not close — a leaking dump valve wastes water continuously and can trigger a low-water condition without latching a fault. Check the Indigo NXT event log for any recent E-codes that cleared automatically before assuming the machine is fault-free.

What does ITP fault mean on a Manitowoc ice machine?

ITP stands for Ice Thickness Probe — the small frequency-based sensor mounted on the evaporator that detects when the ice slab has reached the target thickness and triggers harvest. An ITP fault (event-log code E19, often paired with E31 safe-mode notification) means the probe is reading out of range — typically because mineral scale on the probe surface has detuned its frequency, the probe gap to the evaporator has shifted, or the connector is loose. Soak the ITP in Manitowoc-approved cleaner for 10 minutes, verify the gap matches the service manual, and replace the probe if cleaning does not restore a valid frequency reading.

What does Manitowoc E10 mean and how is it different from E09?

E10 is the flooding-evaporator fault for the second evaporator circuit on dual-TXV / dual-circuit Manitowoc machines, and E09 is the same fault on the first circuit. The control compares compressor discharge-temperature variance between the two circuits to detect liquid floodback. Common root causes on either circuit: a TXV stuck open or with a loose sensing bulb, refrigerant overcharge from a previous service, a leaking harvest valve allowing refrigerant bypass, or scale on the evaporator reducing boil-off. Do not run the machine with active flooding — compressor damage is rapid. Diagnosis is circuit-specific; identify which TXV and harvest valve belong to the faulted circuit before charging or replacing components.

What does Manitowoc E12 (curtain switch fault) mean?

E12 logs when the water-splash curtain switch has been in the open position (curtain absent or switch not actuated) for more than 12 continuous hours — distinct from E11, which is the immediate curtain or refrigeration fault. Most common cause: the curtain was removed during cleaning and not reinstalled. Other causes are a broken curtain tab that no longer presses the position switch, the switch failing in the open state, or a wiring fault back to the control board. Reinstall the curtain, verify the curtain switch LED illuminates on the board when the tab is pressed, and replace the curtain or switch if the LED stays dark.

What does Manitowoc E25 mean and how do I clear it?

E25 is a bin-level low-probe fault — the lowest of the multi-level bin probes that detect ice accumulation in the storage bin. The control reads the low probe as failed (open, shorted, or out of range), so it can no longer trust bin-fill detection. Heavy mineral scale on the probe rod is the most common cause; clean the rod with Manitowoc cleaner and a soft cloth. If cleaning does not restore proper readings, inspect the probe connector at the control board, test continuity from the rod to the connector, and replace the probe assembly if it is bent, cracked, or open-circuit. After repair, monitor for related E26 (medium probe) or E27 (high probe) entries that may indicate a wider wiring issue.

What does Manitowoc E28 (AuCS fault) mean?

E28 is the AuCS — Automatic Cleaning System — fault on Indigo NXT models equipped with the optional AuCS module. The control attempted to communicate with the AuCS module and received no response. Common causes are a loose AuCS communication-cable connector at the control board, an unpowered AuCS module (check the AuCS power supply), a chemical-supply low-level signal stuck on, or an internal AuCS hardware fault. If your machine was not specified with AuCS but logs E28, an old AuCS configuration flag may be set in the controller and needs to be disabled in service mode — consult the model-specific service manual for the parameter.

What do SL1 and SL2 mean on older Manitowoc ice machines?

SL1 and SL2 are safety-limit indicator LEDs on older Manitowoc control boards that pre-date the Indigo / Indigo NXT text-based event log. SL1 illuminates after a long freeze cycle exceeded 45–60 minutes — functionally equivalent to E01 on newer machines (dirty condenser, low charge, scale on the evaporator, or high ambient). SL2 illuminates after a long harvest cycle exceeded 3.5 minutes — functionally equivalent to E02 (failed hot gas valve, low charge, scale on the evaporator, or warm supply water). Diagnose SL1 with a condenser cleaning and pressure check; diagnose SL2 by feeling the harvest line for hot gas during a harvest cycle and descaling the evaporator with nickel-safe cleaner.

How do I read Manitowoc Indigo NXT LED diagnostics and the event log?

Manitowoc Indigo NXT machines surface diagnostics via the front-panel touchscreen — not blinking LEDs. Navigate Menu → Services → Diagnostics for live sensor readings (T1 liquid line, T2 discharge, ITP frequency, water level), and Menu → Services → Event Log for the latched and informational fault history with timestamps. Each event lists the operating conditions captured at trip, which is faster than instrumenting the system from scratch. On legacy Manitowoc boards (Q-series, B-series with discrete LEDs), read the SL1 / SL2 / clean-light pattern instead and consult the model-specific service manual for the LED-to-fault map. Always confirm whether the machine is Indigo, Indigo NXT, NEO, or a legacy controller before applying a fault-code dictionary — the codes differ across families.

Quick Answer

Manitowoc Indigo NXT, Indigo, and NEO ice machines surface faults as E-codes on the touchscreen event log: E01 long freeze, E02 long harvest, E04 high condenser, E10 dual-circuit flooding, E12 curtain switch open, E19/E31 ITP fault and safe-mode, E20 water-system fault, E25–E27 bin-probe faults, E28 AuCS module fault. Legacy Manitowoc boards use SL1 and SL2 indicator LEDs instead.

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By Nichita Herput

Co-founder & CEO · Reviewed May 2026

What error codes does Manitowoc display?

E20

Water-system fault — abnormal water level or flow during fill, circulation, or drain. Clean the inlet-valve screen, sump filter, and water-level probes; test the water pump and drain pump.

E01

Long-freeze fault after six consecutive freeze cycles each exceeded 60 minutes. Almost always a heat-rejection problem — dirty condenser, scale on the evaporator, low refrigerant, or ambient above 90 °F.

E02

Long-harvest fault after three consecutive harvests each exceeded 3.5 minutes. Test the hot gas valve, descale the evaporator with nickel-safe cleaner, and check refrigerant charge and supply-water temperature.

E04

High condenser temperature — T1 liquid-line sensor read above the allowable limit. Clean the condenser coil and filter, verify the condenser fan, check ambient temperature and installation clearances.

E10

Evaporator #2 flooding on dual-TXV machines — TXV #2 stuck open, sensing-bulb loose, refrigerant overcharge in circuit 2, or harvest-valve bypass. Diagnose circuit-specific; do not run with active flooding.

E12

Water-splash curtain switch open for more than 12 hours. Reinstall the curtain, verify the curtain LED illuminates on the control board when the tab is pressed, replace the curtain or switch if needed.

E19

Ice thickness probe (ITP) fault — frequency reading out of range. Soak the probe in Manitowoc cleaner for 10 minutes, verify gap to evaporator, replace the probe if cleaning does not restore valid readings.

E25

Bin-level low-probe fault — control reads the low probe as open, shorted, or out of range. Clean mineral scale from the probe rod, inspect the connector and wiring, replace the probe if continuity tests open.

E28

AuCS (Automatic Cleaning System) fault — control received no response from the AuCS module. Check the AuCS communication-cable connector, AuCS power supply, and chemical-supply level signals.

SL2

Legacy-board safety-limit LED for a long harvest cycle exceeding 3.5 minutes — equivalent to E02 on newer Indigo controls. Test hot gas valve, descale evaporator, verify refrigerant charge.

Common questions about Manitowoc equipment

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