Severity: High
Description: The inverter power module temperature is too high and the unit has shut down to protect the electronics.
Checks:
- Check that the outdoor unit has adequate ventilation and is not obstructed.
- Inspect heat sinks and the inverter area for dust or debris.
- Verify any fans that cool the electronics are running correctly.
Actions:
- Restore airflow and clean components as needed.
- If the error persists, have an engineer test the inverter module and main PCB.
Severity: High
Description: Insufficient water flow has been detected several times and the unit has locked out to protect the system.
Checks:
- Confirm system water pressure is within the recommended range (typically above 1 bar when cold).
- Check that all isolation valves are open and strainers/filters are not blocked.
- Verify the circulation pump is running and properly powered.
Actions:
- Bleed air from the system and clean strainers/filters.
- If flow cannot be restored, contact your installer to investigate pipework or pump sizing.
Severity: Medium
Description: On three-phase models the incoming supply phase order is incorrect or has changed.
Checks:
- Confirm the unit is a three-phase model.
- Check the phase sequence at the isolator with a suitable tester.
- Confirm no recent changes have been made to the supply wiring.
Actions:
- Have a qualified electrician correct the phase order.
- Do not swap phases yourself unless you are suitably qualified.
Severity: Medium
Description: Loss of communication between the hydronic module main control board and the wired controller / user interface.
Checks:
- Check the communication cable is securely connected at both ends.
- Inspect the cable for damage, joints or crushed sections.
- Power-cycle the system to see if communication is restored.
Actions:
- If the fault returns, have an engineer test the controller cable.
- Replace the controller or PCB if communication cannot be re-established.
Severity: Medium
Description: Fault detected on the backup electric heater water outlet temperature sensor.
Checks:
- Inspect the sensor and wiring at the backup heater outlet.
- Check connectors for corrosion or loose contacts.
- Measure sensor resistance and compare with manufacturer values.
Actions:
- Replace the faulty sensor.
- If a new sensor does not clear the error, the control board may need replacement.
Severity: Medium
Description: Fault on the domestic hot water tank temperature sensor.
Checks:
- Check the DHW tank sensor position and ensure it is properly inserted in its pocket.
- Inspect the sensor cable and connector for damage.
- Measure sensor resistance at the PCB terminals.
Actions:
- Re-seat or replace the tank sensor as required.
- If wiring and sensor are OK, have the PCB checked by an engineer.
Severity: Medium
Description: Fault on the refrigerant outlet temperature sensor of the outdoor heat exchanger.
Checks:
- Check the sensor is firmly clipped to the coil or pipe.
- Inspect wiring for damage or disconnection at the outdoor PCB.
- Measure sensor resistance and compare to the temperature table.
Actions:
- Replace the sensor if readings are out of range or intermittent.
- If the error persists, the outdoor PCB may be faulty.
Severity: Medium
Description: Fault on the outdoor ambient air temperature sensor.
Checks:
- Confirm the sensor is located correctly and not influenced by exhaust air or direct sunlight.
- Inspect the cable and connector at the outdoor PCB.
- Measure sensor resistance versus ambient temperature.
Actions:
- Replace the ambient sensor if readings are incorrect.
- Check the PCB input if a new sensor does not resolve the issue.
Severity: Medium
Description: Fault on the upper temperature sensor of the buffer / balance tank.
Checks:
- Verify sensor insertion depth and physical mounting on the tank.
- Inspect wiring back to the hydronic box PCB.
- Measure sensor resistance and compare to specified values.
Actions:
- Reposition or replace the tank sensor.
- If wiring and sensor test good, have the control board assessed.
Severity: High
Description: The flow switch has detected insufficient water flow during operation.
Checks:
- Check system pressure, valves and strainers.
- Confirm the circulation pump is running and correctly vented.
- Look for airlocks or recently closed valves/radiators.
Actions:
- Restore correct flow and reset the unit.
- If E8 recurs frequently, have the hydraulic design and pump selection reviewed.
Severity: Medium
Description: Fault on the compressor suction pipe temperature sensor.
Checks:
- Inspect the sensor mounting on the suction line for good contact and insulation.
- Check wiring between the sensor and outdoor PCB.
- Measure sensor resistance at a known temperature.
Actions:
- Replace the suction sensor if out of specification.
- If the problem remains, further diagnosis of the PCB is required.
Severity: Medium
Description: Fault on the compressor discharge pipe temperature sensor.
Checks:
- Inspect sensor contact and insulation on the discharge line.
- Check for damaged or loose wiring.
- Measure sensor resistance and compare to the temperature table.
Actions:
- Replace the sensor if necessary.
- If error persists with a good sensor, suspect a PCB input fault.
Severity: Medium
Description: Fault on the solar panel or auxiliary temperature sensor (where fitted).
Checks:
- Verify the system actually uses the solar/aux sensor – some installations leave it unused.
- Check sensor wiring and terminals.
- Measure sensor resistance if the sensor is connected.
Actions:
- Disable unused sensor inputs in settings if supported, or fit a dummy sensor where required.
- Replace the sensor if the circuit is in use and readings are incorrect.
Severity: Medium
Description: Fault on the lower temperature sensor of the buffer / balance tank.
Checks:
- Check sensor mounting at the lower position on the tank.
- Inspect the cable for damage or loose connectors.
- Measure sensor resistance and compare to specification.
Actions:
- Re-seat or replace the tank sensor.
- If the fault remains, the sensor input on the PCB may be damaged.
Severity: Medium
Description: Fault on the water side heat exchanger inlet water temperature sensor.
Checks:
- Confirm the sensor is correctly installed on the inlet pipe.
- Inspect wiring between sensor and hydronic PCB.
- Measure sensor resistance at the PCB terminals.
Actions:
- Replace the inlet sensor if defective.
- Have the control board checked if a new sensor does not clear the error.
Severity: High
Description: The controller memory (EEPROM) in the hydronic box is not being read correctly.
Checks:
- Power the unit off completely for several minutes and restart.
- Check all low-voltage connections on the hydronic PCB.
- Confirm supply voltage is stable and within limits.
Actions:
- If the error returns, the hydronic PCB will usually need to be repaired or replaced.
- Contact the manufacturer support channel or your installer.
Severity: High
Description: The inverter DC bus voltage has dropped below the safe operating threshold.
Checks:
- Check mains voltage is within the specified range under load.
- Inspect mains terminals and internal power wiring for loose connections.
- Look for signs of damage or overheating around the inverter module.
Actions:
- Have an electrician check the supply and breaker sizing.
- If supply is sound, the inverter or main PCB may require replacement.
Severity: Medium
Description: Loss of communication between the outdoor unit main control and the hydronic module.
Checks:
- Check the interconnecting communication cable (P/Q or equivalent) for continuity.
- Ensure polarity is correct on communication terminals.
- Inspect for water ingress or corrosion at terminals.
Actions:
- Repair or replace damaged cabling.
- If wiring is sound, an engineer may need to replace one of the PCBs.
Severity: High
Description: The outdoor main controller cannot reliably communicate with the inverter drive module.
Checks:
- Inspect the harness between the main PCB and inverter module.
- Check for LED status indicators on both boards per the service manual.
- Verify supply voltages to the inverter module.
Actions:
- Reseat or replace the harness as needed.
- If the error persists, either the inverter module or outdoor main PCB may be faulty.
Severity: Medium
Description: Fault on the refrigerant outlet (liquid line) sensor of the water side heat exchanger.
Checks:
- Check the sensor clamp and insulation on the liquid line.
- Inspect wiring back to the outdoor PCB.
- Measure sensor resistance against the temperature chart.
Actions:
- Replace the sensor if readings are incorrect.
- If still faulty, investigate the PCB input.
Severity: Medium
Description: Fault on the refrigerant inlet (gas line) sensor of the water side heat exchanger.
Checks:
- Inspect sensor mounting on the suction/gas line.
- Check cable and connector condition.
- Measure sensor resistance at a known temperature.
Actions:
- Install a new sensor if defective.
- If a good sensor does not clear the code, suspect the controller.
Severity: High
Description: Inverter protection (such as L0/L1) has occurred multiple times in a defined period.
Checks:
- Review error history for associated L-codes (L0, L1, etc.).
- Check mains voltage stability and wiring.
- Inspect the outdoor unit for blocked airflow or mechanical issues causing overload.
Actions:
- Resolve underlying L-code causes before resetting.
- If inverter trips recur, the drive module may need replacement.
Severity: Medium
Description: Fault on the room / internal air temperature sensor used for space heating control.
Checks:
- Check the position of the room sensor or controller in the dwelling.
- Inspect the cable for damage or dislodged plugs.
- Measure sensor resistance and compare to specification.
Actions:
- Relocate or replace the sensor as needed.
- If using a third-party room thermostat, confirm wiring and settings.
Severity: High
Description: The outdoor DC fan has failed to run or is outside normal speed limits.
Checks:
- Check that the fan rotates freely and is not obstructed by ice or debris.
- Inspect fan connector and wiring at the outdoor PCB.
- Look for signs of water ingress or burnt components on the fan or PCB.
Actions:
- Replace the fan motor if it does not run when powered.
- If a new fan does not resolve it, further diagnose the outdoor PCB or inverter.
Severity: High
Description: The supply voltage is outside the acceptable range for the unit.
Checks:
- Measure line voltage at the unit terminals under load.
- Check for undersized cable or long runs causing voltage drop.
- Confirm there are no frequent brownouts or overvoltage events.
Actions:
- Correct wiring or upgrade supply as required.
- If voltage is within spec and the error continues, check the voltage sensing circuit on the PCB.
Severity: High
Description: The refrigerant pressure sensor signal is missing or out of range.
Checks:
- Inspect the high-pressure sensor connection on the outdoor unit.
- Check wiring for shorts, opens or corrosion.
- Compare measured sensor output to expected values if equipment is available.
Actions:
- Replace the pressure sensor if the signal is invalid.
- If a new sensor does not help, the controller input may be defective.
Severity: Medium
Description: Fault on the second heating zone water outlet temperature sensor.
Checks:
- Confirm that a second zone is actually used and wired.
- Inspect sensor position on the zone 2 outlet pipe.
- Check continuity of the sensor cable.
Actions:
- Install or replace the zone 2 sensor as needed.
- If unused, some controllers allow the input to be disabled in settings.
Severity: Medium
Description: Fault on the main water side heat exchanger outlet temperature sensor.
Checks:
- Check sensor placement on the flow pipe leaving the unit.
- Inspect wiring between sensor and hydronic PCB.
- Measure resistance and compare with temperature.
Actions:
- Replace the outlet sensor if defective.
- Investigate the control board if the error persists with a good sensor.
Severity: Medium
Description: The unit has locked out after repeated PP protection events with very low outlet water temperature.
Checks:
- Review system design for low return water temperatures (e.g. underfloor, large emitters).
- Check for excessive flow or bypasses that may cause over-cooling.
- Verify sensor readings for water inlet and outlet.
Actions:
- Adjust flow rates and control settings to keep outlet within safe limits.
- If problem persists, consult the system designer to review emitter sizing and hydraulics.
Severity: High
Description: The EEPROM associated with the refrigerant system or inverter module cannot be read correctly.
Checks:
- Power the unit off fully and restart.
- Check connectors on the inverter module and main PCB.
- Verify there is no visible damage to memory devices on the board.
Actions:
- If the error remains, the inverter module or associated PCB will likely need replacement.
- Engage manufacturer technical support for board replacement procedures.
Severity: High
Description: H6 fan protection has occurred many times in a short period and the unit has locked out.
Checks:
- Resolve root cause of H6 (fan or PCB fault) before resetting.
- Check that the fan can run through several cycles without tripping.
- Inspect for intermittent wiring or contact issues.
Actions:
- After repairs, clear the error and test operation thoroughly.
- If HH reappears, detailed diagnostics of the outdoor electronics are required.
Severity: High
Description: The system has seen repeated low-pressure protection events over a set time period.
Checks:
- Check refrigerant charge and look for signs of leakage.
- Verify water flow and air flow across the heat exchangers.
- Inspect strainers, filters and fan operation.
Actions:
- Have an F-gas engineer leak-test and recharge if necessary.
- Address any flow issues before returning the unit to normal service.
Severity: High
Description: Refrigerant pressure has dropped below the minimum safe level.
Checks:
- Check for insufficient load or very low water temperatures.
- Inspect for signs of refrigerant leaks (oil stains, hissing, bubbles).
- Verify that strainers and filters are clean and pumps/fans are operating.
Actions:
- Do not keep resetting the unit – have an F-gas qualified engineer check the system.
- Restore correct refrigerant charge and fix any leaks.
Severity: High
Description: Refrigerant pressure has exceeded the maximum safe level.
Checks:
- Ensure outdoor coil and any air paths are clean and unobstructed.
- Check that all water circuits are flowing and valves are open.
- Verify that the system is not being run outside its specified temperature range.
Actions:
- Clean coils and restore design water flow.
- If pressures remain high, an engineer should check expansion valve operation and refrigerant charge.
Severity: High
Description: The compressor current has exceeded the allowed limit.
Checks:
- Check mains voltage and phase balance (for three-phase models).
- Listen for mechanical noises suggesting compressor mechanical problems.
- Inspect wiring and contactors for overheating.
Actions:
- Have an engineer measure running current and insulation resistance.
- Replace compressor or inverter components if necessary.
Severity: High
Description: The compressor discharge temperature has risen above the protection threshold.
Checks:
- Check outdoor airflow and ensure fans and coils are clean.
- Verify correct water flow and leaving water temperature.
- Check refrigerant charge and look for restrictions in the circuit.
Actions:
- Correct any airflow or flow issues and reset the unit.
- If overheating persists, a refrigeration engineer should investigate further.
Severity: High
Description: The temperature difference between water inlet and outlet is too large.
Checks:
- Check water flow rate through the unit – a low flow will give a large temperature difference.
- Verify all valves are open and strainers are clean.
- Confirm the system is not blocked or air-locked.
Actions:
- Increase flow rate by adjusting pump speed or valves.
- Flush and balance the system if necessary.
Severity: High
Description: The inverter has detected an internal fault or overload condition.
Checks:
- Check supply voltage and cabling.
- Inspect outdoor PCB and inverter module for visible damage.
- Look for associated L-codes that indicate the detailed cause.
Actions:
- If supply and load conditions are normal, the inverter module may need replacement.
- Contact an authorised service partner before replacing boards.
Severity: High
Description: General inverter module protection event.
Checks:
- Review operating conditions when the fault occurred (ambient, load, mode).
- Check supply voltage and wiring.
- Inspect for blocked coils or seized fans that could overload the inverter.
Actions:
- Address system-side causes (air/water flow, wiring).
- If the inverter continues to trip, it may require replacement.
Severity: High
Description: The DC bus voltage is too low for safe inverter operation.
Checks:
- Measure incoming mains voltage under load.
- Check for loose terminals, undersized cable or long runs.
- Inspect rectifier and DC link components for damage.
Actions:
- Correct supply issues and retest.
- If supply is sound, the inverter/rectifier section may need replacement.
Severity: High
Description: The DC bus voltage has risen above the safe limit.
Checks:
- Check that the supply is not over-voltage.
- Verify that power-factor and braking components are functioning correctly.
- Confirm there are no wiring errors or incorrect connections.
Actions:
- Have an electrician verify supply quality.
- Replace damaged inverter components if over-voltage has occurred internally.
Severity: High
Description: Internal motor control (MCE) fault in the inverter drive.
Checks:
- Power-cycle the unit and check if the error reoccurs immediately.
- Inspect inverter PCB for signs of damage.
- Confirm cooling of the inverter is adequate.
Actions:
- If L4 repeats, the inverter module will usually need replacement.
- Consult manufacturer technical support before replacing expensive boards.
Severity: High
Description: The inverter detects that the compressor speed is not increasing as commanded.
Checks:
- Check for a seized compressor or mechanical blockage.
- Verify correct wiring between inverter and compressor.
- Listen for unusual noises or failure to start.
Actions:
- Do not keep forcing restarts on a seized compressor.
- Have a refrigeration engineer assess the compressor and inverter.
Severity: Medium
Description: Phase sequence or phase detection error linked to the inverter protection system.
Checks:
- Confirm three-phase supply phase order is correct.
- Check for loose or missing phases at the isolator or breaker.
- Inspect wiring between terminals and inverter board.
Actions:
- Correct any supply wiring issues.
- If supply is correct, the inverter’s phase-detection circuitry may be faulty.
Severity: High
Description: The compressor frequency has changed too quickly, indicating instability or control issues.
Checks:
- Review system settings for unrealistic capacity or curve settings.
- Check supply voltage stability.
- Inspect inverter and compressor connections.
Actions:
- After confirming system conditions, replace the inverter if L8 persists.
- Log conditions when the error occurs to aid diagnosis.