Carel Error Codes: E0, E1, Etc and CHt on ir33, SmartCella and UltraCella

On Carel controllers, E0 to E4 are probe faults, but the probe names depend on the controller. On ir33, MasterCella and SmartCella, E0 is the room probe S1 and E1 the defrost probe S2. On UltraCella, E0 to E4 are probes B1 to B5. HI and LO are temperature alarms, Etc is a clock fault, and CHt is a high condenser temperature alarm that needs a manual reset.

The tables below come from Carel's own user manuals for UltraCella, the ir33 platform, SmartCella and the easy range. Check the model name on the front of the controller before using a table, because the same code can point to a different probe.

At a glance

Code	What Carel says it means	What to do first
E0	Room probe S1 fault (probe B1 on UltraCella)	Call an engineer. On the ir33, the compressor switches to a timed duty cycle
E1	Defrost probe S2 fault (probe B2 on UltraCella)	Call an engineer
E2, E3, E4	Probe S3, S4 or S5 fault (B3, B4 or B5 on UltraCella)	Call an engineer
HI	High temperature alarm	Check the door, the load and the condenser
LO	Low temperature alarm	Check the set point and call an engineer if it persists
cht	High condenser temperature pre-alarm	Clean the condenser and clear its airflow
CHt	High condenser temperature alarm	The compressor stops. Fix the cause, then reset manually
Etc	Real time clock fault	Call an engineer to check the clock and settings
EE, EF	EEPROM error, unit or operating parameters	Call an engineer

Source: Carel ir33 platform and UltraCella user manuals, alarms and signals tables.

How Carel shows an alarm

Carel's UltraCella user manual explains that the alarm message appears on the display while the bell icon blinks and the buzzer sounds, and that several alarms are shown in sequence. On the easy range, the message flashes alternately with the temperature. Carel adds one detail for easy controllers: E0 stays steady, with no temperature shown, if it is the only active alarm.

The probe naming is the main source of confusion. UltraCella calls its probes B1 to B5, while the ir33 platform, MasterCella and SmartCella call them S1 to S5. S1 and S2 are probe names, not codes, so a list that treats them as codes has mixed the two up.

ir33, MasterCella and SmartCella codes

The ir33 platform covers ir33, ir33 power, ir33 DIN, powercompact and MasterCella. This table comes from Carel's ir33 platform user manual, and Carel's SmartCella instruction sheet uses the same codes.

Code	What Carel says it means	Reset	What happens
rE	Virtual control probe fault	Automatic	Compressor runs on the duty setting (parameter c4)
E0	Room probe S1 fault	Automatic	Compressor runs on the duty setting (parameter c4)
E1	Defrost probe S2 fault	Automatic	Functions unchanged
E2, E3, E4	Probe S3, S4 or S5 fault	Automatic	Functions unchanged
___	Probe not enabled	Automatic	Not a fault
LO	Low temperature alarm	Automatic	Functions unchanged
HI	High temperature alarm	Automatic	Functions unchanged
AFr	Antifreeze alarm	Manual	Compressor off
IA	Immediate alarm from external contact	Automatic	Compressor runs on the duty setting (parameter A6)
dA	Delayed alarm from external contact	Automatic	Depends on the controller settings
dEF	Defrost running	Automatic	Not a fault
Ed1, Ed2	Defrost on evaporator 1 or 2 ended by timeout	Automatic or manual	Functions unchanged
Pd	Maximum pump down time alarm	Automatic or manual	Functions unchanged
LP	Low pressure alarm	Automatic or manual	Compressor off
AtS	Autostart in pump down	Automatic or manual	Functions unchanged
cht	High condenser temperature pre-alarm	Automatic or manual	Functions unchanged
CHt	High condenser temperature alarm	Manual	Compressor and defrost off
dor	Door open too long alarm	Automatic	Functions unchanged
Etc	Real time clock fault	Automatic or manual	Functions unchanged
EE	E2prom error, unit parameters	Automatic	Compressor and fans off, defrost not performed
EF	E2prom error, operating parameters	Automatic	Compressor off
HA, HF	HACCP alarm, HA or HF type	Manual	Functions unchanged
n1 to n6	Alarm on unit 1 to 6 in the network

On SmartCella, Carel describes HA as the maximum temperature threshold being exceeded, and HF as a power failure lasting over a minute after which the maximum threshold was exceeded.

UltraCella codes

UltraCella is Carel's cold room controller. These come from the alarm table in the UltraCella user manual, where every alarm activates the alarm relay and buzzer.

Code	What Carel says it means	Reset
rE	Virtual control probe fault	Automatic
E0	Probe B1 fault	Automatic
E1	Probe B2 fault	Automatic
E2	Probe B3 fault	Automatic
E3	Probe B4 fault	Automatic
E4	Probe B5 fault	Automatic
LO	Low temperature alarm	Automatic
HI	High temperature alarm	Automatic
IA	Immediate alarm from external contact	Automatic
SA	Serious alarm from external contact	Automatic
Pd	Maximum pump down time alarm	Automatic
LP	Low pressure alarm	Automatic
AtS	Autostart in pump down	Automatic or manual
CHt	High condenser temperature alarm	Manual
dor	Door open too long alarm	Automatic
Etc	Real time clock is broken	Automatic
EE	EEprom error, unit parameters	Automatic
EF	Eeprom error, operating parameters	Automatic
Ed1, Ed2	Defrost ended by timeout	Automatic
HA, HF	HACCP alarm, HA or HF type	Manual
LoG	Download recorded temperature fault	Automatic
uPL, dnL	Parameters upload or download fault	Automatic
SOF	Software update fault	Automatic

UltraCella units fitted with an electronic expansion valve or a three-phase module add further codes, such as SHA for low superheat protection, EEA for a valve motor fault and EPE for an off-line three-phase module. Those are for an engineer to diagnose.

Carel easy codes

The easy, easy compact and easy split controllers have a shorter list. These come from Carel's easy user manual.

Code	What Carel says it means
E0	Probe 1 error, the control probe
E1	Probe 2 error, the defrost probe
E2	Probe 3 error, the condenser or product probe
LO, HI	Low or high temperature alarm
dOr	Open door alarm
EE	Unit parameter error
EF	Operating parameter error
Ed	Defrost ended by timeout
dF	Defrost running
cht	Dirty condenser pre-alarm
CHt	Dirty condenser alarm
EtC	Clock alarm
SrC	Maintenance request signal (easy split only)

There is no E3 on the easy range. Carel also says that if EE appears often or stays for some time, the controller should be checked, because its original precision may not be guaranteed.

E0 and E1 explained

E0 and E1 are the most searched Carel codes, and both mean the controller has lost a temperature reading, usually because a probe or its cable has failed or come loose. E0 matters more. With the room probe gone, the ir33 can no longer control to temperature, so it runs the compressor on a timed duty cycle set by parameter c4. That keeps some cooling going, but the room or cabinet is no longer held at its set point, so keep an eye on the stock. E1 leaves the main functions unchanged, because the defrost probe only tells the controller when to end a defrost.

cht and CHt

Carel uses the lower-case cht for a high condenser temperature pre-alarm and the capital CHt for the full alarm. On the easy range, Carel describes them as dirty condenser alarms. The pre-alarm is a warning, but on the ir33, CHt switches off the compressor and defrost, and it needs a manual reset once the cause has been dealt with. A blocked or dirty condenser and a hot plant room are the usual places to look.

How to silence and reset a Carel alarm

• UltraCella. Carel says to press the Alarm key to silence the buzzer and deactivate the alarm relay. Alarms with automatic reset clear once the cause has gone. For manual reset alarms, remove the cause first, then press the Alarm button.
• ir33 platform. The PRG/MUTE button silences the buzzer and deactivates the alarm relay. Carel says manual reset alarms can be reset by pressing two buttons together for more than 5 seconds once the cause has gone. The manual for your model shows which two.
• easy. Pressing SET silences the buzzer, but the code and the alarm relay only clear when the cause is resolved. Every easy alarm resets automatically apart from CHt, which needs the controller switching off and on with the UP button or the power disconnecting.

What you can check safely

• The door. HI and dor often follow a door left open or not sealing.
• The condenser. With cht or CHt, check the condenser is not blocked and is reasonably clean, and that the plant room is not unusually hot.
• The load. Make sure stock is not packed against the evaporator or blocking the airflow.
• The stock. With a probe fault, HI or a HACCP alarm, check the product temperature with a separate thermometer.

Safety

Carel's ir33 manual says only qualified personnel may install or carry out technical service on the product, and warns that incorrect connection of the power supply may seriously damage the system. It also asks that the circuits are kept dry, because liquids and condensate contain corrosive minerals that can damage them. Carel notes that food safety programmes based on HACCP require the devices used for food preservation to be checked periodically, so their measuring errors stay within the allowed limits. Our guide to cold room temperature monitoring covers what that means in practice.

When to call an engineer

• Any probe fault from E0 to E4, or rE.
• CHt that returns after the condenser has been cleaned.
• LP, Pd or AtS, which point to the refrigeration side.
• EE, EF or Etc, which affect the controller's settings and clock.
• HI that returns with the door shut and the load arranged properly.

Our cold room repair team works on rooms run by Carel controllers across London, and our cold room diagnostic guide walks through what an engineer checks when a room will not hold temperature.

Questions people ask about Carel error codes

What does E0 mean on a Carel controller?

E0 is a probe fault. On ir33, MasterCella and SmartCella, it is the room probe S1, and the compressor switches to a timed duty cycle. On UltraCella, it is probe B1, and on the easy range, probe 1, the control probe. It needs an engineer.

What does E1 mean on a Carel?

E1 is the defrost probe S2 on the ir33 platform and SmartCella, probe B2 on UltraCella and probe 2 on the easy range. The main functions carry on, but the probe needs replacing or reconnecting.

What does E3 mean on a Carel controller?

E3 is a probe S4 fault on the ir33 platform and a probe B4 fault on UltraCella. The easy range has no E3.

What does Etc mean on a Carel?

Etc is a real time clock fault, which UltraCella's manual calls "Real time clock is broken". The clock runs timed functions such as defrosts and HACCP logging, so an engineer should check it.

What is a CHt alarm on a Carel?

CHt is the high condenser temperature alarm, described on the easy range as a dirty condenser alarm. It stops the compressor and needs a manual reset after the cause is fixed. The lower-case cht is the pre-alarm that comes first.

How do I reset a Carel alarm?

Silence it first: the Alarm key on UltraCella, PRG/MUTE on the ir33 platform or SET on easy. Most alarms reset themselves when the cause clears. Manual reset alarms such as CHt need the cause fixing and then a reset, which differs by controller.

Keeping a Carel-controlled room on temperature

Identify the controller, read the code, and remember that most Carel codes clear themselves once the cause has gone. A probe fault or a CHt that keeps returning needs an engineer, and planned refrigeration maintenance keeps condensers clean and probes checked before they cause an alarm.

Last updated: 4 November 2026