- Heat pumps
- Air-to-water heat pump
PJ04
Daikin Altherma 4 H F PJ-04: outdoor inverter PCB mismatch
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
Daikin Altherma 4 H F code PJ-04 means Inverter PCB mismatch, which stops the heat pump and requires a manual reset. Check [11] Malfunctioning on the indoor display, note any recent PCB replacement or service work on the outdoor unit, and call your Daikin installer.
Safety first
Stop and check this first
- Do not open the outdoor unit or switch box cover to look at the inverter PCB: the outdoor unit contains flammable R290 refrigerant and high-voltage capacitors that require more than 10 minutes after power disconnection to drop below 50 V DC.
Safe checks you can perform
- Read the PJ-04 long description in [11] Malfunctioning and check for companion PJ codes
- Check whether the outdoor unit recently had a PCB replacement, commissioning, or repair visit
- Leave the manual reset of PJ-04 to the technician and verify [5.23] Emergency selection
Leave these tasks to a qualified professional
- Do not attempt this professional task: Verify inverter PCB part number, harness connections, and model configuration per the service manual
- Do not attempt this professional task: Perform the manual reset after correcting the inverter PCB mismatch and verify operation
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.
Verify inverter PCB part number, harness connections, and model configuration per the service manual
What they doWith mains power disconnected for more than 10 minutes and capacitor voltage measured below 50 V DC, the Daikin certified technician inspects the outdoor unit inverter PCB and main PCB (A1P) part numbers, connectors, and model configuration following the Daikin service manual guideline for PJ-04.
They must show youthe multimeter reading below 50 V DC before opening the inverter assembly and the verified PCB part number compared with the outdoor unit model nameplate.
In writingthe outdoor unit model code, the installed inverter PCB part reference, the service manual check results for PJ-04, and the root cause of the mismatch.
Perform the manual reset after correcting the inverter PCB mismatch and verify operation
What they doOnce the correct inverter PCB or board configuration is installed and all switch box covers are closed, the technician performs the manual reset shown on the user interface and runs a full heating or hot water test cycle.
They must show youthe [11] Malfunctioning screen cleared of PJ-04 and normal compressor operation on the user interface.
In writingthe replacement PCB part number (if replaced), the manual reset timestamp, and confirmation that PJ-04 did not recur in [11] Malfunction history.
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.
Read the PJ-04 long description in [11] Malfunctioning and check for companion PJ codes
- Who:
- You, from the indoor unit touchscreen without opening any equipment panels.
- How:
- Go to [11] Malfunctioning, tap PJ-04 to open its long description, and check [11] Malfunction history (with advanced end user permission) to see whether PJ-01 (Capacity setting mismatch) or PJ-09 (Fan 1 mismatch) was logged at the same time.
- Result that matters:
- Seeing whether PJ-04 is isolated to the inverter PCB or accompanied by other unit/component mismatch codes in the PJ group.
- If PJ-01 or PJ-09 appears alongside PJ-04, that points to a broader outdoor unit model configuration or multi-board spare-part mismatch.
- If PJ-04 is the only active code in [11] Malfunctioning, that isolates the fault to the inverter PCB mismatch condition for the technician to check in the service manual.
- Evidence to keep:
- Keep a clear photo of the [11] Malfunctioning screen showing PJ-04, its timestamp, and the full long description.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Check whether the outdoor unit recently had a PCB replacement, commissioning, or repair visit
- Who:
- You, by reviewing your installation or service paperwork without using tools.
- How:
- Check your recent service invoices or commissioning records, and read the model information in [6.6] Information > About to note whether PJ-04 appeared right after an installer or technician worked on the outdoor unit.
- Result that matters:
- Whether the inverter PCB mismatch started immediately after an electrical or board intervention on the outdoor unit.
- If PJ-04 appeared right after a service visit or board swap, that strongly points to a spare-part reference or configuration mismatch that the servicing company must verify.
- If no one has opened or serviced the unit since commissioning, that rules out a wrong replacement part and indicates an internal inverter PCB identification fault.
- Evidence to keep:
- Write down the date of any recent service work, the company name, and the model details shown in [6.6] About.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Leave the manual reset of PJ-04 to the technician and verify [5.23] Emergency selection
- Who:
- You, at the indoor user interface while keeping all circuit breakers in the ON position.
- How:
- Do not repeatedly reset PJ-04 or switch off the outdoor and indoor circuit breakers; instead, check [5.23] Settings > Emergency selection if you need backup electrical heating or hot water while waiting for the technician listed in [6.2] Dealer information.
- Result that matters:
- Daikin states in section 14.4 that it is important to understand the problem and take measures before resetting an error code, and section 2.2 of the operation manual warns not to turn off the circuit breakers.
- If PJ-04 was already reset once and immediately stopped the heat pump again, that confirms a hard inverter PCB mismatch that cannot be cleared from the user interface.
- If you leave PJ-04 unreset and enable backup heating via [5.23] Emergency selection, that keeps hot water and space heating available while preserving the diagnostic history.
- Evidence to keep:
- Record the number of reset attempts (if any) and the dealer contact details from [6.2] Information > Dealer information.
Never open the outdoor unit casing or switch box to inspect the inverter PCB yourself; internal capacitors hold hazardous DC voltage and the unit contains R290 refrigerant.
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 PJ-04
- code erreur Daikin Altherma PJ-04
- codice PJ-04 pompa di calore Daikin
- código PJ-04 bomba de calor Daikin
- Daikin Altherma error PJ-04
- Daikin Altherma Fehler PJ-04
- Daikin heat pump code PJ-04
- Daikin PJ-04
- Daikin Wärmepumpe Fehlercode PJ-04
- défaut PJ-04 pompe à chaleur Daikin
- error Daikin Altherma PJ-04
- errore Daikin Altherma PJ-04
What it means
In chapter 14.4.4 of the Daikin Altherma 4 H F installer reference guide (4PEN773391-1C, page 213), error code PJ-04 is defined with both Title and Trigger as Inverter PCB mismatch, Effect as Heat pump will stop operating, and Reset as Manual. It sits in the PJ mismatch group between PJ-01 (Capacity setting mismatch, Wrong combination of units) and PJ-09 (Fan 1 mismatch). Because the installer reference guide provides only the mismatch summary and directs technicians to the service manual for detailed troubleshooting, code PJ-04 alone does not prove that the inverter PCB is broken rather than mismatched in spare-part specification, jumper/configuration state, or inter-board wiring.
Warnings and stop conditions
- Highsource verified
Do not open the outdoor unit or switch box cover to look at the inverter PCB: the outdoor unit contains flammable R290 refrigerant and high-voltage capacitors that require more than 10 minutes after power disconnection to drop 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
Symptoms and causes
Probable causes · in order
- Inverter PCB specification or configuration mismatch after outdoor unit board replacement or serviceCommon
Daikin's error table defines PJ-04 as Inverter PCB mismatch, which commonly surfaces when an outdoor unit inverter PCB or main PCB (A1P) is replaced or serviced and its variant or configuration does not match the unit model.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Persistent inverter PCB identification or communication mismatch requiring service manual diagnosisPossible
If no board was recently changed and PJ-04 locks out the heat pump on a manual reset, the outdoor controller cannot validate the inverter PCB identity and requires the detailed troubleshooting guideline in the Daikin service manual.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does PJ04 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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