Blood warmers

Smiths Medical HL-90: troubleshooting and error codes

The ServiceForge knowledge base holds 35 documented symptoms for the Smiths Medical HL-90, with 74 ranked causes, 83 diagnostic checks with test points and expected values, and 0 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Over Temperature alarm triggers continuously patient safety

Over Temperature alarm sounds and remains on during operation

Ranked causes

1. Insufficient recirculating solution flow due to kinked warming set (common)
2. Airlock in Fluid Warming Set (common)
3. Pump seized (occasional)
4. Triac short circuit (occasional)
5. Opto defective (occasional)
6. Thermistor defective (occasional)
7. Over Temperature alarm set point too low (occasional)
8. Unit accidentally filled with hot recirculating solution (rare)
9. Ambient temperature too high (rare)

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

Over temperature alarm continuously on caution

Alarm condition triggered; fluid warming system is overheating or alarm setpoint is too low.

Ranked causes

1. Insufficient recirculating solution flow (common)
2. Triac short circuit (occasional)
3. Opto defective (occasional)
4. Thermistor defective (occasional)
5. Over temperature alarm setpoint too low (rare)
6. Unit filled with hot recirculating solution (rare)
7. Ambient temperature too high (rare)

First check

Visually inspect Warming Set for kinks

Test point: Warming Set tubing
Expected: straight with free flow

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

Fluid Warming Set Interlock alarm triggers continuously caution

Fluid Warming Set Interlock alarm sounds and remains on

Ranked causes

1. Microswitch not being made; set not fitted correctly (common)
2. Microswitch lever out of shape (occasional)
3. Microswitch is faulty (occasional)
4. Wiring or PCB fault (occasional)

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

Fluid Warming Set interlock alarm continuously on caution

Alarm indicating Warming Set is detected as not properly installed or microswitch is stuck; Warming Set may not be fitted correctly.

Ranked causes

1. Fluid Warming Set not fitted correctly (common)
2. Microswitch lever out of shape or faulty microswitch (occasional)
3. Wiring or PCB fault at J3 connector (rare)

First check

Verify Warming Set is firmly seated

Test point: Warming Set connector
Expected: set seated fully and firmly

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

Fluid Warming Set Interlock alarm not working caution

Fluid Warming Set Interlock alarm does not trigger when it should

Ranked causes

1. Microswitch lever stuck (common)
2. Defective microswitch (occasional)
3. Wiring or PCB fault (occasional)

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

No electrical power to unit

Unit is not receiving mains power; all indicators are off

Ranked causes

1. Power cord unplugged or unit switched off (common)
2. Fuse F1 or F2 blown (common)
3. Transformer open circuit or F3 blown (occasional)

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

Recirculating Solution Level alarm triggers continuously caution

Recirculating Solution Level alarm sounds and remains on

Ranked causes

1. Recirculating solution is actually low (common)
2. Sticky float switch (occasional)
3. Wiring or PCB fault (occasional)

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

Unit has no power high voltage

Unit does not power on; mains supply or internal power distribution failure.

Ranked causes

1. Unit not plugged in or socket not live (common)
2. Fuse F1 or F2 blown (common)
3. Transformer open circuit or fuse F3 blown (occasional)

First check

Verify unit is plugged in and turned on

Test point: power switch and mains connector
Expected: unit switched on, plugged into live socket

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

Unit will not heat up caution

No heat output or insufficient heating; thermostat, triac, heater, or setpoint may be faulty.

Ranked causes

1. Bad thermostat, triac or heater element (common)
2. Idle temperature setpoint too low (occasional)
3. Ambient temperature too high (rare)

First check

Test thermostat, triac and heater element

Test point: heating circuit components
Expected: all components functional and properly connected

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

Unit will not heat up caution

Unit does not reach desired temperature or provide heat

Ranked causes

1. Bad T-Stat, Triac or Heater (common)
2. Idle temperature set point too low (occasional)
3. Ambient temperature too high (rare)

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

Calibration: Temperature display accuracy

Verify displayed recirculating solution temperature matches actual temperature measured at heater element outlet.

Ranked causes

1. Temperature calibration drift or offset (common)
2. Over-temperature alarm malfunction (occasional)

First check

Verify ambient room temperature within operating range

Test point: Room environment
Expected: 22.0°C ± 2.0°C, ±2.0°C
Tools: Room thermometer

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

Floating or erratic LCD reading caution

LCD display shows unstable or drifting numerical values

Ranked causes

1. Bad LCD unit (common)
2. Bad 5V regulator (occasional)

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

Fluid Warming Set interlock alarm not working caution

Alarm not triggering when expected; microswitch stuck or not operating, or wiring fault.

Ranked causes

1. Microswitch lever stuck (occasional)
2. Defective microswitch or wiring fault (occasional)

First check

Check microswitch lever operation

Test point: microswitch lever
Expected: lever moves freely, makes and breaks contact

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

LCD display reading floating or erratic

LCD display shows unstable or changing values; LCD unit or 5V regulator may be faulty.

Ranked causes

1. Bad LCD unit (occasional)
2. Bad 5V regulator (occasional)

First check

Test LCD display by substitution

Test point: LCD display unit
Expected: stable, consistent reading with correct value

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

Over temperature alarm not working caution

Display reads correctly but alarm is not triggering; thermistor or alarm setpoint may be at fault.

Ranked causes

1. Over temperature alarm setpoint too high (common)
2. Thermistor defective or display not reading correctly (occasional)

First check

Verify over temperature alarm setpoint

Test point: alarm setpoint setting
Expected: appropriate threshold for application

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

Over Temperature alarm not working patient safety

Over Temperature alarm does not trigger when it should

Ranked causes

1. Display reading correctly but alarm set point too high (common)
2. Display not reading correctly; thermistor defective (occasional)

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

Recirculating solution level alarm continuously on caution

Low solution level alarm triggered; actual solution level may be low or float switch may be stuck.

Ranked causes

1. Recirculating solution is actually low (common)
2. Sticky float switch or wiring fault (occasional)

First check

Visually inspect recirculating solution level

Test point: solution reservoir level
Expected: above minimum level mark

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

Recirculating Solution Level alarm not working caution

Recirculating Solution Level alarm does not trigger when solution is low

Ranked causes

1. Defective float switch (common)
2. Wiring or PCB fault (occasional)

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

Calibration: nominal temperature set point patient safety

Adjustment of water temperature nominal set point to 40°C or 42°C depending on territory

Ranked causes

1. Territory-specific nominal temperature configuration required (common)

First check

Verify water temperature at 40°C nominal set point

Test point: Water temperature sensor
Expected: 39.9°C to 41.1°C, -0.1 to +1.1°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 verification

Verify temperature calibration of the HOTLINE blood warmer unit meets specifications

Ranked causes

1. Annual calibration maintenance requirement (common)

First check

Allow unit to stabilize temperature during normal operation

Test point: Display
Expected: Temperature gradually rising towards 41°C

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

Disposable set interlock alarm test failure patient safety

Unit does not trigger interlock alarm and associated indicators when disposable set is disconnected

Ranked causes

1. Disposable set interlock alarm system malfunction (unknown)

First check

Gently ease disposable set away from interlock block

Test point: Disposable set connector
Expected: Alarm triggers before full disconnection

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

General alarm test failure patient safety

Unit does not trigger all alarm indicators and audible alert when general alarm test button pressed

Ranked causes

1. Alarm system malfunction (unknown)

First check

Verify GREEN LED extinguishes

Test point: GREEN LED indicator
Expected: LED extinguished

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

Maintenance: O-Ring seal replacement

Replace O-Ring seals in disposable interface block connector as part of annual maintenance

Ranked causes

1. Scheduled annual O-Ring seal replacement (common)

First check

Remove socket head screws

Test point: Disposable interface block
Expected: All screws removed
Tools: 1/8-inch Allen key

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

Maintenance: Recirculating solution change (distilled water)

Drain and replace distilled water recirculating solution at 30-day intervals

Ranked causes

1. Scheduled 30-day recirculating solution change (common)

First check

Unplug the unit from power supply

Test point: Mains power
Expected: Unit disconnected from electricity

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

Maintenance: Recirculating solution change (isopropyl alcohol) caution

Drain and replace 35% isopropyl alcohol recirculating solution at 30-day intervals

Ranked causes

1. Scheduled 30-day recirculating solution change (common)

First check

Prepare two batches of 1.4 litres solution per Formula 2

Test point: Solution preparation
Expected: Formula 2: 700ml 70% isopropyl alcohol PLUS 700ml distilled water, prepared twice litres

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

Over temperature alarm test failure patient safety

Unit does not trigger over temperature alarm and associated indicators when over temperature alarm test button is held

Ranked causes

1. Over temperature alarm system malfunction (unknown)

First check

Verify display temperature rises

Test point: Temperature display
Expected: 43°C - 44°C, to 44°C

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

Recirculating solution leaks at Warming Set connector caution

Fluid leaking from connection between unit and Warming Set; O-rings worn or degraded.

Ranked causes

1. Worn O-rings at connector (common)

First check

Inspect O-rings for wear or degradation

Test point: O-rings on unit and Warming Set connector
Expected: O-rings intact and not cracked or deformed

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

Recirculating solution leaks at Warming Set connector caution

Fluid leaks from the connection point between the warming set and the unit

Ranked causes

1. Worn O-rings (common)

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

Recirculating solution level alarm not working caution

Alarm not triggering when solution level is low; float switch defective or wiring fault.

Ranked causes

1. Defective float switch or wiring fault (occasional)

First check

Test float switch operation at low level

Test point: float switch
Expected: makes contact when solution is low

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

Recirculating solution level alarm test failure patient safety

Unit does not trigger low level alarm and associated indicators when float switch is depressed

Ranked causes

1. Recirculating solution level alarm system malfunction (unknown)

First check

Depress float switch arm using non-magnetic tool

Test point: Float switch
Expected: Switch depressed without magnetic attraction

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

Recirculating solution replacement (Hydrogen Peroxide) caution

Replace 0.3% Hydrogen Peroxide recirculating solution at annual service interval

Ranked causes

1. Hydrogen Peroxide solution degradation at 12-month interval (common)

First check

Prepare two 1.4 litre batches of 0.3% Hydrogen Peroxide solution per formula

Test point: Solution mixing area
Expected: Two batches of 1.4 litres each, 0.3% Hydrogen Peroxide concentration

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

Recirculating solution replacement (Isopropyl Alcohol) caution

Replace Isopropyl Alcohol disinfectant solution at 30-day intervals if Hydrogen Peroxide unavailable

Ranked causes

1. Isopropyl Alcohol solution potency loss at 30 days (common)

First check

Prepare two 1.4 litre batches of Isopropyl Alcohol solution (Formula 2) immediately before use

Test point: Solution mixing area
Expected: Two fresh batches prepared per Formula 2, used same day

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

Temperature verification check

Verify displayed temperature matches actual recirculating solution temperature without full calibration

Ranked causes

1. Display temperature does not match actual temperature (occasional)

First check

Attach TEMP CHECK thermometer to interlock block and Disposable Set

Test point: Interlock block connector
Expected: TEMP CHECK properly connected to measure solution flow temperature

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

Warming Set hard to install

Warming Set connector difficult to insert into unit socket; O-rings may be dry or damaged.

Ranked causes

1. Dry O-rings on connector (common)

First check

Inspect O-rings for dryness or deterioration

Test point: O-rings on Warming Set connector
Expected: flexible and lubricated

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

Warming Set hard to install caution

Fluid Warming Set is difficult to connect to the unit

Ranked causes

1. Dry O-rings (common)

1 corrective action and part numbers 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.