- Heat pumps
- Air-to-water heat pump
L1-03
Daikin Altherma 4 H F L1-03: inverter PCB current offset fault
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
On a Daikin Altherma 4 H F heat pump, L1-03 indicates a malfunction of the inverter PCB triggered by a current offset error, stopping the heat pump with a manual reset. Check [11] Malfunction history and [5.23] Emergency selection on the indoor display, and call your authorised installer.
Safety first
Stop and check this first
- Never remove the outdoor unit cover or touch the inverter PCB when L1-03 appears: the outdoor unit contains flammable R290 refrigerant, and main circuit capacitors retain lethal DC voltage until the power supply has been disconnected for more than 10 minutes and measured below 50 V DC.
- Do not switch off the unit circuit breakers or cycle power repeatedly to bypass a manual-reset code like L1-03: Daikin warns that circuit breakers must stay ON after commissioning to keep protective functions active.
Safe checks you can perform
- Check [11] Malfunctioning and [11] Malfunction history for L1-02 or other L1 codes
- Record active operation mode in [6.5] and sensor temperatures in [6.3]
- Check backup heating takeover in [5.23] Emergency selection and call [6.2]
Leave these tasks to a qualified professional
- Do not attempt this professional task: Discharge capacitors below 50 V DC and diagnose the inverter PCB and current transformer T1A
- Do not attempt this professional task: Reset L1-03 manually and verify compressor startup in [7.3] Operation test run
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.
Discharge capacitors below 50 V DC and diagnose the inverter PCB and current transformer T1A
What they doAn authorised Daikin technician disconnects the power supply for more than 10 minutes, verifies with a multimeter that main circuit capacitor voltage is less than 50 V DC, inspects outdoor unit connectors X*A/X*Y, current transformer T1A, and inverter PCB A1P, and follows the Daikin service manual troubleshooting procedure for L1-03.
They must show youthe measured capacitor voltage below 50 V DC and the inspection results for current transformer T1A, connectors X*A/X*Y, and the inverter PCB.
In writingthe service manual test results for L1-03 and, if a component is replaced, its exact Daikin part reference and diagnostic justification.
Reset L1-03 manually and verify compressor startup in [7.3] Operation test run
What they doOnce the cause of the current offset error is corrected and the switch box cover is secured, the technician performs the manual reset of L1-03 and runs [7.3] Maintenance mode > Operation test run to confirm the inverter starts and runs the compressor without logging new L1 codes.
They must show youthe [11] Malfunctioning screen clear of L1-03 while the heat pump operates during the [7.3] test run.
In writingthe [7.3] Operation test run result, confirmation that Maintenance mode was exited, and the clean post-test error log.
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 [11] Malfunction history for L1-02 or other L1 codes
- Who:
- You, inspecting L1-03 on the indoor unit touchscreen with advanced end user permission.
- How:
- Open [11] Malfunctioning and tap L1-03 to read the full help text, then inspect [11] Malfunction history to see whether L1-02 (Current sensor error), L1-01, or L1-04 was logged around the same time.
- Result that matters:
- Whether the outdoor unit recorded only a current offset error (L1-03) or multiple inverter current and power module errors.
- If L1-02 appears alongside L1-03 in the history list, that confirms both current sensor error and current offset error triggered on the inverter current-measurement chain.
- If L1-03 is the only code present, that isolates the stop to the current offset check and rules out assuming the PCB is dead before the technician inspects connectors and T1A.
- Evidence to keep:
- Keep a clear photograph of the [11] Malfunctioning help text and the timestamped [11] Malfunction history list.
Do not try to reset L1-03 repeatedly from the user interface; Daikin instructs users to understand the problem and take measures before resetting an error code.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Record active operation mode in [6.5] and sensor temperatures in [6.3]
- Who:
- You, reading out information from the indoor touchscreen menu [6] Information.
- How:
- Go to [6.5] Information > Operation modes and [6.3] Information > Sensors to note what mode was active (space heating, cooling, or domestic hot water) and the outdoor and leaving water temperatures when L1-03 occurred.
- Result that matters:
- Giving the service technician the exact operating state and electrical context at the moment L1-03 tripped.
- If L1-03 coincided with a household power flicker or electrical disturbance, that points to a transient event at inverter startup that you should report to the installer.
- If L1-03 appeared during steady operation with stable household power, that confirms the current offset error triggered under normal operating conditions.
- Evidence to keep:
- Write down the active mode from [6.5], the outside and water temperatures from [6.3], and the time of the stop.
Never open the outdoor unit service cover to inspect main PCB A1P or current transformer T1A yourself.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Check backup heating takeover in [5.23] Emergency selection and call [6.2]
- Who:
- You, from the indoor unit user interface while leaving all circuit breakers ON.
- How:
- Open [5.23] Settings > Emergency selection to check whether the electrical heater (backup heater, booster heater, or tank boiler if applicable) is set to take over during a heat pump failure, and read your installer number in [6.2] Dealer information.
- Result that matters:
- Maintaining space heating or domestic hot water safely via the electrical heater until the technician diagnoses L1-03.
- If Emergency selection allows automatic takeover or you acknowledge the manual takeover pop-up, that confirms the electrical heater will cover heating and hot water at higher electricity consumption.
- If takeover is set to Manual or reduced modes without acknowledgment, that indicates space heating or domestic hot water remains off while only frost protection and freeze prevention stay active.
- Evidence to keep:
- Save a photo of the [5.23] Emergency selection screen and log your call to the number in [6.2] Dealer information.
After commissioning, do not turn off the circuit breakers to the units: keeping breakers ON maintains R290 leak detection, water pipe freeze prevention, and anti-blockage protections.
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 L1-03
- code erreur Daikin Altherma L1-03
- codice L1-03 pompa di calore Daikin
- código L1-03 bomba de calor Daikin
- Daikin Altherma error L1-03
- Daikin Altherma Fehler L1-03
- Daikin heat pump code L1-03
- Daikin L1-03
- Daikin Wärmepumpe Fehlercode L1-03
- défaut L1-03 pompe à chaleur Daikin
- error Daikin Altherma L1-03
- errore Daikin Altherma L1-03
What it means
In Daikin installer reference guide 4PEN773391-1C (Chapter 14, section 14.4.4, page 209), error code L1-03 is assigned to Malfunction of INV PCB with the trigger Malfunction of INV PCB: Current offset error, stopping heat pump operation under a manual reset. It shares the manual-reset inverter PCB group with L1-01 (instantaneous overcurrent at boot waveform), L1-02 (current sensor error), L1-04 (IGBT / power module error), L1-05 (jumper setting error), and L1-06 (SP/MP-PAM overvoltage), where the outdoor wiring diagram includes main PCB A1P, current transformer T1A, and connectors X*A/X*Y. Code L1-03 alone does not prove the inverter PCB is defective without testing the current-sensing path.
Warnings and stop conditions
- Highsource verified
Never remove the outdoor unit cover or touch the inverter PCB when L1-03 appears: the outdoor unit contains flammable R290 refrigerant, and main circuit capacitors retain lethal DC voltage until the power supply has been disconnected for more than 10 minutes and measured below 50 V DC.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- Mediumsource verified
Do not switch off the unit circuit breakers or cycle power repeatedly to bypass a manual-reset code like L1-03: Daikin warns that circuit breakers must stay ON after commissioning to keep protective functions active.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Symptoms and causes
Probable causes · in order
- Current offset deviation detected on the outdoor unit inverter PCBPossible
During inverter current baseline checking, the outdoor controller detects a current offset error on the inverter PCB stage and halts heat pump operation until a technician diagnoses the circuit per the service manual.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Connection or signal fault in the current transformer T1A and X*A/X*Y harnessPossible
Because the outdoor unit wiring layout pairs main board A1P with current transformer T1A and connectors X*A/X*Y, a loose connector or degraded current sensor signal (related to neighbour code L1-02) can disturb current offset readings.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does L1-03 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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