Respiratory humidifiers

Fisher & Paykel Healthcare MR700: troubleshooting and error codes

The ServiceForge knowledge base holds 36 documented symptoms for the Fisher & Paykel Healthcare MR700, with 84 ranked causes, 81 diagnostic checks with test points and expected values, and 16 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Excessive water in circuit patient safety

Rainout or water accumulation in breathing circuit tubing

Ranked causes

1. Water trap not at lowest point (non-heated mode) (common)
2. Heater wire too close to temperature probe (occasional)
3. Circuit cooled by external air conditioner (occasional)
4. Chamber control set too high (occasional)
5. Maximum permissible peak flow rate of chamber exceeded (occasional)
6. Humidifier chamber tilted (common)
7. Faulty temperature probe (low resistance) (rare)
8. Inspiratory heater wire not connected in parallel dual circuit (occasional)

First check

Verify chamber level

Test point: Humidification chamber
Expected: Chamber level and stable

1 more check with pass and fail actions, 8 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low temperature alarm patient safety

Airway or chamber temperature drops below set threshold; alarm activates

Ranked causes

1. Gas flow stopped or interrupted (common)
2. Set temperature increased by more than 2°C (occasional)
3. Temperature probe not in probe housing (common)
4. Gas flow rate too low (occasional)
5. Excessive distance between heater wire and temperature probe (occasional)
6. Poor thermal contact between chamber base and heater plate (occasional)
7. Temperature probe not inserted at chamber outlet (occasional)
8. Heater element needs replacement (rare)

First check

Verify gas flow to humidifier

Test point: Gas inlet
Expected: Gas flowing continuously

2 more checks with pass and fail actions, 8 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Temperature probe disconnected or faulty patient safety

Display shows '- - -' with flashing red Temperature Probe LED and audio alarm. Various fault patterns shown by decimal point sequences indicate open/short circuits.

Ranked causes

1. Temperature probe not plugged in or open circuit chamber outlet probe (common)
2. Open circuit in common lead in probe cable (occasional)
3. Open circuit patient airway probe (occasional)
4. Short circuit chamber outlet probe (occasional)
5. Short circuit patient airway probe (occasional)
6. Short in probe cable between airway and chamber probes (rare)

First check

Observe display pattern for fault type identification

Test point: Airway temperature display
Expected: '- - -' with no decimal points = probe not plugged in or open chamber probe

2 more checks with pass and fail actions, 6 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

High temperature alarm patient safety

Airway or chamber temperature rises above set threshold; alarm activates

Ranked causes

1. Sudden spurious increase in gas flow (occasional)
2. Heater wire too close to temperature probe (common)
3. Faulty EOH sensor on temperature probe (low resistance) (rare)
4. No water in chamber (common)
5. Faulty TOP sensor on temperature probe (low resistance) (rare)

First check

Verify water level in chamber

Test point: Humidification chamber
Expected: Water present at proper level

1 more check with pass and fail actions, 5 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Breathing circuit leak patient safety

Loss of pressure or gas leakage from breathing circuit connections

Ranked causes

1. Faulty circuit connections (common)
2. No water bag connected (common)
3. Temperature probes incorrectly fitted (occasional)
4. Chamber filler stopper missing (occasional)

First check

Inspect all breathing circuit connections

Test point: Circuit connectors
Expected: All connections seated and secure

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Heater wire alarm while temperature displayed caution

Heater wire alarm activates but temperature is still shown on display

Ranked causes

1. Heater wire unplugged (common)
2. Heater wire broken (occasional)
3. Heater wire switch turned off but wire connected (common)
4. Heater wire switch on but not connected (occasional)

First check

Verify heater wire connection

Test point: Heater wire connector
Expected: Connector fully seated and secure

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low humidity patient safety

Humidifier output humidity insufficient for patient needs

Ranked causes

1. Chamber control set too low (common)
2. No water in humidification chamber (common)
3. Chamber temperature too low (occasional)
4. Gas flow rate too high for chamber capacity (occasional)

First check

Verify water level in chamber

Test point: Humidification chamber
Expected: Water present at appropriate level

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Temperature fluctuating patient safety

High and low temperature alarms alternate; temperature control unstable

Ranked causes

1. Ventilation rate too low or too erratic (common)
2. External heating or cooling influence (occasional)
3. Temperature probes incorrectly positioned (common)
4. Faulty temperature probe (intermittent open or short) (occasional)

First check

Verify temperature probe position

Test point: Breathing circuit
Expected: Probe positioned correctly at outlet or airway

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No temperature display, no alarm patient safety

Temperature is not displayed and no alarm lights are active

Ranked causes

1. Humidifier voltage rating incorrect (common)
2. Heaterplate overheat protector operated (occasional)
3. Transformer overheat protector operated (rare)

First check

Verify mains voltage rating

Test point: Unit label / mains supply
Expected: Unit voltage rating matches supply voltage

1 more check with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Temperature probe alarm patient safety

Display shows '---' indicating temperature probe disconnection or fault

Ranked causes

1. Temperature probe unplugged (common)
2. Temperature probe plug dirty (common)
3. Temperature probe faulty (occasional)

First check

Verify temperature probe connection

Test point: Probe connector
Expected: Probe connector fully seated and secure

1 more check with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Airway temperature too high (heater wire mode) patient safety

Red Airway Temp High LED flashes and audio alarm sounds when gas temperature is 2 °C higher than Temperature Control setting. Both heater circuits immediately disabled.

Ranked causes

1. Temperature control setting too high (common)
2. Heater malfunction causing overheating (occasional)

First check

Monitor airway temperature reading against Temperature Control setting

Test point: Airway temperature display
Expected: Airway temperature within 2 °C of Temperature Control setting, ≤ 2 °C

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Airway temperature too low (heater wire mode) patient safety

Red Airway Temp Low LED flashes and audio alarm sounds when gas temperature is 2 °C lower (4 °C for MR720) than Temperature Control setting. If condition persists >100 seconds, heater circuits shut off. Mute button silences alarm and resumes heat for 100 seconds.

Ranked causes

1. Insufficient heater output (common)
2. Heater wire or heaterplate malfunction (occasional)

First check

Monitor airway temperature reading against Temperature Control setting

Test point: Airway temperature display
Expected: Airway temperature within 2 °C (MR700) or 4 °C (MR720) of Temperature Control setting, ≥ -2 °C

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Airway temperature too low (non-heater wire mode) patient safety

Red Airway Temp Low LED flashes. Audio alarm sounds after 30 second delay. Pressing mute silences alarm for 10 minutes and restores heaterplate power during that time. If temperature drops below 5 °C, display shows 'LO' and audio alarm sounds.

Ranked causes

1. Insufficient heaterplate output (common)
2. Heaterplate malfunction (occasional)

First check

Monitor airway temperature reading

Test point: Airway temperature display
Expected: Airway temperature ≥ 29.5 °C, > 29.5 °C

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Temperature measurement

Calibration of VR4 (41 °C comparator) and VR5 (A-to-D converter span) after PCB service or E0x-E7x errors

Ranked causes

1. PCB repair or replacement affecting ±5V rails or A-to-D converter (common)
2. E0x to E7x error messages displayed (common)

First check

Verify unit warm-up time

Test point: Unit operation time
Expected: at least twenty minutes

9 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Chamber temperature too high patient safety

Chamber Temp High amber LED flashes and audio alarm sounds (can be muted). Heater circuits switch off. Triggered when chamber outlet gas exceeds chamber set temperature by >4 °C for >20 minutes, or by ≥10 °C immediately.

Ranked causes

1. Chamber set temperature too high (common)
2. Heater malfunction causing chamber overheating (occasional)

First check

Monitor chamber outlet temperature against chamber set temperature

Test point: Chamber temperature sensor reading
Expected: Chamber outlet temp within 4 °C of chamber set temperature, ≤ 4 °C

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Chamber temperature too low patient safety

Chamber Temp Low amber LED flashes and audio alarm sounds. Triggered by two criteria depending on set temperature: <4 °C below set temp for >20 min (if set <35 °C), or <31 °C for >20 min (if set ≥35 °C).

Ranked causes

1. Insufficient heater output or set temperature too low (common)
2. Heater malfunction or insufficient heating (occasional)

First check

Monitor chamber outlet temperature relative to chamber set temperature

Test point: Chamber temperature sensor reading
Expected: If set <35 °C: outlet ≥ (set - 4 °C); if set ≥35 °C: outlet ≥ 31 °C

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Heater wire disconnected or faulty (MR700/720/730) caution

Heater Wire alarm LED flashes, audio alarm sounds. Both heater wire and heaterplate circuits shut down. Display may show 'F-2' if fuse is open.

Ranked causes

1. Heater wire disconnected (common)
2. F2 fuse open circuit (occasional)

First check

Check heater wire physical connection

Test point: Heater wire connector
Expected: Heater wire firmly seated and undamaged

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

No temperature display with 'see manual' indicator patient safety

No temperature display shown and 'see manual' indicator light is on

Ranked causes

1. Control PCB fault from water damage (occasional)
2. Failed self test with control PCB issue (occasional)

First check

Inspect control PCB for water or contamination

Test point: Control PCB
Expected: PCB clean and dry, no corrosion or damage

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Set low warning active caution

Set Low amber LED enabled continuously (no audio alarm). Version 1.0/2.0: triggered if chamber set <31.0 °C. Version 3.0: triggered if chamber set <34.0 °C or Temperature Control setting <34.0 °C.

Ranked causes

1. Chamber set temperature below minimum threshold (common)
2. Temperature Control setting below minimum (Version 3.0 software) (occasional)

First check

Check software version and chamber set temperature

Test point: Software version and chamber set temperature display
Expected: v1.0/2.0: chamber set ≥31.0 °C; v3.0: chamber set ≥34.0 °C and Temperature Control ≥34.0 °C

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

41°C overheat calibration fault caution

41°C overheat protection circuit calibration out of limits

Ranked causes

1. 41°C comparator calibration out of limits (rare)

First check

Verify 41°C comparator calibration

Test point: Overheat protection circuit
Expected: Calibration within specification

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Airway temperature too high (non-heater wire mode) patient safety

Red Airway Temp High LED flashes and audio alarm sounds when gas temperature is 41 °C or higher. Heaterplate power immediately shut off.

Ranked causes

1. Heaterplate set temperature too high (common)

First check

Monitor airway temperature

Test point: Airway temperature display
Expected: Airway temperature < 41 °C, < 41 °C

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm LED flashing without audible sound patient safety

Alarm LED is blinking but no audible alarm tone is heard

Ranked causes

1. Mute switch has been pressed (common)

First check

Check mute switch status

Test point: Mute button / display
Expected: Mute mode inactive or timer expired

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Airway temperature control

Set airway temperature from 31 to 40 °C using front panel control knob. Resolution 0.1 °C; display flashes for 5 seconds after adjustment.

Ranked causes

1. Airway temperature adjustment required (unknown)

First check

Set airway temperature

Test point: Front panel Temperature Control knob
Expected: Display shows selected temperature (31 to 40 °C) flashing for 5 seconds °C minimum, 31 to 40 °C range

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Chamber control (heater wire mode)

Adjust chamber outlet temperature offset from airway temperature. Range -5 to +2 °C in 0.5 °C steps (heater wire mode only). Fixed knob option available to prevent inadvertent adjustment.

Ranked causes

1. Chamber outlet temperature offset adjustment required (unknown)

First check

Set chamber control offset

Test point: Front panel Chamber Control knob (heater wire mode only)
Expected: Display shows offset value (-5 to +2 °C) flashing for 5 seconds °C minimum, -5 to +2 °C range

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Heater wire mode selection caution

Select heater wire mode (MR720, MR730 only) using latching push switch. Green LED indicates heater wire mode active. Audible beep confirms mode change. Alarm triggers if mode switched with heater wire disconnected.

Ranked causes

1. Heater wire mode enabled/disabled (unknown)

First check

Verify heater wire mode selection

Test point: Front panel Heater Wire Switch and adjacent green LED
Expected: Green LED on for heater wire mode; LED off for non-heater wire mode; audible beep confirms change

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Power-up sequence verification (Version 1.0)

Verify complete power-up sequence for Version 1.0 software: watchdog test, display test, temperature and chamber settings, software version, heater plate setting, and audio beep. Each displays for 2 seconds.

Ranked causes

1. Power-up sequence check required (unknown)

First check

Watchdog circuit test

Test point: Power-on sequence display
Expected: SEE MANUAL LED lights briefly

6 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Power-up sequence verification (Version 2.0/3.0)

Verify complete power-up sequence for Version 2.0 and 3.0 software: watchdog test, display test, model number, software version, temperature setting, chamber setting, heater plate setting, and audio beep. Each displays for 2 seconds with momentary blanking.

Ranked causes

1. Power-up sequence check required (unknown)

First check

Watchdog circuit test

Test point: Power-on sequence display
Expected: SEE MANUAL LED lights briefly

7 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Warm-up mode (heater wire mode)

Verify warm-up mode exiting conditions for heater wire mode (MR700, MR730 all versions, MR720 v1.0). Low temperature alarm disabled during warm-up; enabled when exiting. Mode exits when: airway temp within 0.8 °C of setpoint, OR no increase in 4 min (2 min v3.0), OR not within 2 °C after 10 min.

Ranked causes

1. Warm-up mode operation and exit conditions (unknown)

First check

Monitor airway temperature during warm-up

Test point: Front panel airway temperature display
Expected: Temperature rises from initial value toward setpoint

3 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Calibration: Warm-up mode (non-heater wire mode)

Verify warm-up mode exiting conditions for non-heater wire mode (MR730/MR720 v1.0, MR480). Low temperature alarm disabled during warm-up; enabled when exiting. Mode exits when: airway temp above 30 °C, OR no increase in 15 min, OR 2 °C increase in 15 min but not 30 °C after further 15 min.

Ranked causes

1. Warm-up mode operation and exit conditions (non-heater wire) (unknown)

First check

Monitor airway temperature during warm-up

Test point: Front panel airway temperature display
Expected: Temperature above 30 °C

3 more checks with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

External water leak - disposable chamber caution

Water leaking from disposable humidification chamber exterior

Ranked causes

1. Chamber used beyond lifespan (common)

First check

Check chamber age and condition

Test point: Disposable chamber
Expected: Chamber within service life, no cracks or damage

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

External water leak - reusable chamber caution

Water leaking from reusable humidification chamber exterior

Ranked causes

1. Chamber O-ring faulty (occasional)

First check

Inspect chamber O-ring

Test point: Chamber seal
Expected: O-ring clean, undamaged and properly seated

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Heater wire alarm with F2 display caution

Heater wire alarm activates with 'F2' fault code displayed

Ranked causes

1. Internal fuse blown (rare)

First check

Visual fuse inspection if accessible

Test point: Internal fuses F1-F4
Expected: Fuses intact and properly seated

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Heater wire connected in non-heater wire mode caution

Heater Wire alarm LED flashes and audio alarm sounds. Indicates a heater wire has been connected when non-heater-wire mode is selected (Heater Wire 'On' LED is off). Heaterplate is switched off.

Ranked causes

1. Heater wire incorrectly connected in non-heater wire mode (common)

First check

Verify operating mode and heater wire connection status

Test point: Heater Wire 'On' LED and physical heater wire connection
Expected: If non-heater-wire mode: no heater wire connected; if heater-wire mode: heater wire connected

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

MR480 jumper cable connection (Revision D or earlier)

Special cable connection required for MR480 model during calibration

Ranked causes

1. MR480 calibration jumper requirement (common)

First check

Install MR480 jumper cable

Test point: Pin 7 of U10 to cathode of D7
Expected: Jumper cable connected with 22 kΩ resistor in series

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Set Low LED on caution

'Set Low' LED is illuminated on the control display

Ranked causes

1. Chamber or airway temperature control setting too low (common)

First check

Review temperature control setting

Test point: Control display setting
Expected: Setting appropriate for clinical requirement

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Standby LED flashing patient safety

Standby indicator LED is blinking on the humidifier display

Ranked causes

1. Humidifier in standby mode (common)

First check

Verify standby mode status

Test point: Standby LED / mode button
Expected: Standby mode inactive

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Error codes

Code	Meaning	Trigger	Severity
`- - -`	Temperature probe not plugged in or low temperature (~0 °C)	Temperature probe disconnected at connector or open circuit chamber outlet probe	error
`- - -.`	Open circuit in common lead of probe cable	Open circuit detected in common lead of probe cable	error
`-.- -`	Short in probe cable between patient airway and chamber outlet probes	Short circuit detected between patient airway probe and chamber outlet probe in cable	error
`---`	Temperature sensor probe fault	Probe signal absent, shorted, or out of range	error
`b-1`	Mute button stuck on at turn on or held > 5 minutes	Mute button remains pressed at power-on or continuously for over 5 minutes	warning
`b-2`	Standby button is on	Standby button pressed or stuck	warning
`Ec`	Checksum error; possible failure of U1 EPROM	Microprocessor detects checksum mismatch during EPROM read	critical
`En`	Memory test error; possible failure of U4 RAM	Microprocessor detects RAM test failure on U4	critical
`EP1`	Hardware fault; Q13 short not effective	Software-driven shorted probe cable test detects Q13 short circuit failure	error
`EP2`	Low probe temperature (~0 °C)	Probe temperature reading abnormally low during shorted probe cable test	warning
`EP3`	High probe temperature (~70 °C)	Probe temperature reading abnormally high during shorted probe cable test	warning
`EP4`	Partial short between active probe cable conductors	Shorted probe cable test detects capacitive coupling or partial short	warning
`EXx`	ADC overflow or underflow error at multiplexer stage X (0-7); x=o for overflow, x=u for underflow	ADC counts exceed expected range at indicated multiplexer stage	error
`F-2`	Open circuit heater wire fuse (MR700/720/730 only)	Heater wire fuse F2 is open circuit or defective	error
`F-2`	Heater Wire fuse F2 is open circuited	Fuse F2 fails during heater wire operation	error
`LO`	Airway temperature below 5 °C	Airway temperature drops below 5 °C in either heater wire or non-heater wire mode	critical

Likely causes and actions for each code are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.