- Heat pumps
- Air-to-water heat pump
L5-00
Daikin Altherma 4 H F L5-00: inverter DC output overcurrent
Risk level
High
Professional inspection is recommended.
Urgency
Immediate
Quick answer
Code L5-00 on a Daikin Altherma 4 H F means the outdoor unit detected an instantaneous output overcurrent in the inverter DC section and stopped the heat pump on a manual reset. Record the timestamp in [11] Malfunctioning, avoid repeated resets, and call your Daikin installer.
Safety first
Stop and check this first
- Never open the outdoor unit or touch components inside the switch box. Even with power off, main circuit capacitors retain lethal voltage; a technician must wait more than 10 minutes after disconnecting power and measure less than 50 V DC before touching electrical parts.
- Never bypass safety protections or repeatedly force manual resets on L5-00; re-energizing an unverified DC overcurrent fault can destroy the inverter power module or compressor windings.
Safe checks you can perform
- Check [11] Malfunctioning and Malfunction history for companion L8, L9, or P3 codes
- Do not force repeated resets or toggle circuit breakers on L5-00
- Confirm emergency heating in [5.23] and call the installer listed in [6.2]
Leave these tasks to a qualified professional
- Do not attempt this professional task: Replace any failed power component, perform the manual reset, and verify DC current under load
- Do not attempt this professional task: Isolate power for over 10 minutes, confirm <50 V DC, and test the inverter DC section and compressor leads
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Replace any failed power component, perform the manual reset, and verify DC current under load
What they doAfter repairing the fault identified in the inverter DC section or compressor circuit, the technician must manually reset L5-00, run a supervised heating or hot water cycle, and verify that DC current remains within specification.
They must show youthe live operating status during compressor ramp-up and the [11] Malfunction history confirming L5-00 does not recur.
In writingthe root cause of the DC output overcurrent, the part number of any replaced PCB or component, and the post-repair test duration.
Isolate power for over 10 minutes, confirm <50 V DC, and test the inverter DC section and compressor leads
What they doA Daikin certified technician must switch off the main power supply, wait more than 10 minutes, verify less than 50 V DC across the main circuit capacitors, and measure inverter power module diodes/IGBTs along with compressor winding resistance and insulation.
They must show youthe multimeter reading below 50 V DC prior to touching switch box parts and the resistance and insulation test readings on the compressor harness and inverter PCB.
In writingthe residual DC link voltage (V DC), compressor winding and earth insulation readings (ohms / MOhm), and the test result of the inverter DC section.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Check [11] Malfunctioning and Malfunction history for companion L8, L9, or P3 codes
- Who:
- You at the indoor user interface with user permission set to advanced end user.
- How:
- Open [11] Malfunctioning to read the long description for L5-00, then open [11]: Malfunction history to see whether L5-00 was preceded by P3-01, P3-04, L8-05, L9-01, or U2-01.
- Result that matters:
- Whether L5-00 happened as a single event or followed repeated DC current or stall warnings.
- If the malfunction history shows prior P3-01, P3-04, L8-05, or L9-01 entries before L5-00, that confirms a recurring inverter current or compressor load fault.
- If L5-00 is a single entry with no prior current warnings, that suggests an abrupt transient trip that still requires professional inspection before resetting.
- Evidence to keep:
- Capture a photo of the [11] Malfunctioning screen and the complete [11]: Malfunction history list with timestamps.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Do not force repeated resets or toggle circuit breakers on L5-00
- Who:
- You as the system owner managing the indoor user interface and household panel.
- How:
- Leave the outdoor and indoor circuit breakers ON to preserve freeze protection, and do not repeatedly reset L5-00 or power-cycle the mains.
- Result that matters:
- Protecting the inverter DC section and compressor windings from repeated high-current fault starts.
- If L5-00 was already reset once and returned immediately on compressor start, that confirms a hard fault in the inverter DC output path and you must stop all reset attempts.
- If L5-00 has not been reset yet, leaving the lockout untouched isolates the fault state for the technician's electrical diagnosis.
- Evidence to keep:
- Write down whether any reset was attempted and how many seconds elapsed before L5-00 reappeared.
Never open the outdoor switch box or turn off unit circuit breakers after commissioning; Daikin requires finding why a protection activated before resetting.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Confirm emergency heating in [5.23] and call the installer listed in [6.2]
- Who:
- You using the indoor touchscreen menus while the heat pump is stopped.
- How:
- Check [5.23] Settings > Emergency selection to verify whether the backup heater or booster heater can supply space heating and domestic hot water, then open [6.2] Information > Dealer information.
- Result that matters:
- Keeping indoor heating and hot water running safely via the backup heater while awaiting a Daikin service visit.
- If the emergency selection setting activates the backup heater automatically or via the manual pop-up, that confirms auxiliary electric heating is operating while the outdoor unit remains locked out.
- If no backup heating starts and the sensor water temperature keeps dropping, that indicates you need urgent service from the contact in [6.2].
- Evidence to keep:
- Record the [6.3] water temperature reading, the [5.23] setting, and the service reference from your call to the dealer in [6.2].
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Heat pumps
- Brand
- Daikin
- Product type
- Air-to-water heat pump
Known code variants
- Altherma 4 H F L5-00
- code erreur Daikin Altherma L5-00
- codice L5-00 pompa di calore Daikin
- código L5-00 bomba de calor Daikin
- Daikin Altherma error L5-00
- Daikin Altherma Fehler L5-00
- Daikin heat pump code L5-00
- Daikin L5-00
- Daikin Wärmepumpe Fehlercode L5-00
- défaut L5-00 pompe à chaleur Daikin
- error Daikin Altherma L5-00
- errore Daikin Altherma L5-00
What it means
In chapter 14.4.4 of the Daikin Altherma 4 H F installer reference guide (4PEN773391-1C), L5-00 is titled OU: Inverter instantaneous overcurrent (DC) with the trigger An output overcurrent is detected by checking the current that flows in the inverter DC section. When this protection trips, the heat pump stops operating and requires a manual reset, distinguishing it from automatic-reset DC limit codes (P3-01, P3-04) and supply voltage overcurrent (U2-31). Because a DC output spike can originate from a compressor load stall, wiring insulation breakdown, or power module fault, L5-00 alone never proves which component failed.
Warnings and stop conditions
- Highsource verified
Never open the outdoor unit or touch components inside the switch box. Even with power off, main circuit capacitors retain lethal voltage; a technician must wait more than 10 minutes after disconnecting power and measure less than 50 V DC before touching electrical parts.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- Highsource verified
Never bypass safety protections or repeatedly force manual resets on L5-00; re-energizing an unverified DC overcurrent fault can destroy the inverter power module or compressor windings.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Symptoms and causes
Probable causes · in order
- Sudden compressor load spike or mechanical stall demand on the inverter outputPossible
A rapid pressure rise or compressor stall condition (related to L9-01 stall prevention) draws excessive current through the outdoor inverter DC section and trips L5-00.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Short circuit, insulation breakdown, or loose connection on the inverter output harnessPossible
Damaged motor lead insulation, moisture ingress, or a degraded power connection between the outdoor inverter PCB and the compressor creates an instantaneous DC output overcurrent.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Internal IGBT or power module defect on the outdoor inverter PCBPossible
A failing power switching stage on the outdoor inverter PCB (tracked alongside L1-00 IGBT/power module errors and L8-05 time-limited overcurrent) triggers an immediate L5-00 lockout.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does L5-00 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Daikin Europe N.V. · 2026 · official_doc
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