- Heat pumps
- Air-to-water heat pump
U2-07
Daikin Altherma 4 H F U2-07: supply voltage converter error
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
On Daikin Altherma 4 H F heat pumps, U2-07 is a supply voltage error triggered by a converter error that stops the heat pump and requires a power cycle reset. Photograph U2-07 in [11] Malfunctioning, avoid switching off the circuit breakers yourself, and call your installer.
Safety first
Stop and check this first
- Never repeatedly turn the heat pump circuit breakers OFF and ON to clear U2-07: turning off the breakers disables the R290 leak detection protection and does not fix an underlying converter or supply voltage fault.
- Before inspecting the switch box or converter wiring, the technician must disconnect the unit from the mains by turning off the respective circuit breaker to prevent electrocution.
Safe checks you can perform
- Record the U2-07 message in [11] Malfunctioning and check [11] Malfunction history
- Do not cycle the circuit breakers yourself to force a power-cycle reset
- Verify backup heating status in [5.23] Emergency selection
Leave these tasks to a qualified professional
- Do not attempt this professional task: Diagnose the converter and inverter PCB with the Daikin service manual if U2-07 recurs
- Do not attempt this professional task: Inspect supply voltage and switch box before executing a controlled power cycle
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.
Diagnose the converter and inverter PCB with the Daikin service manual if U2-07 recurs
What they doIf U2-07 returns after the controlled power cycle with verified mains voltage, a Daikin certified technician must disconnect mains power and follow the service manual troubleshooting procedure for U2-07 to test the converter circuit and replace any failed board.
They must show youthe service manual test values for the converter stage and the cleared [11] Malfunctioning screen after repair.
In writingthe specific converter test results, the part number of any PCB or component replaced, and the post-repair test run log.
Inspect supply voltage and switch box before executing a controlled power cycle
What they doA qualified installer must measure the outdoor unit supply voltage against the identification label, switch off the circuit breaker to inspect terminal block X1M for loose connections, restore power, wait the 5 minutes initialization period, and check whether U2-07 clears.
They must show youthe measured supply voltage, the switch box inspection result, and the user interface status after the 5 minutes initialization.
In writingthe voltage readings, the time of the controlled power cycle, and whether U2-07 cleared or returned.
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.
Record the U2-07 message in [11] Malfunctioning and check [11] Malfunction history
- Who:
- You, using the indoor unit touchscreen.
- How:
- Open [11] Malfunctioning, tap U2-07 to read the full error description, and check [11] Malfunction history (available with advanced end user permission) for earlier occurrences.
- Result that matters:
- Documenting the exact U2-07 converter error and any accompanying supply voltage codes before a power cycle clears active volatile state.
- If other U2 supply voltage codes or P1/P3 codes appear in the history around the same time, that points to an incoming power quality or phase balance issue.
- If U2-07 is the only logged code, that narrows the investigation to the converter error trigger and its power supply feed.
- Evidence to keep:
- Take a photo of the U2-07 long description and the timestamped entries in [11] Malfunction history.
Never open the outdoor unit casing or electrical switch box; internal inspection carries electrocution and R290 refrigerant hazards.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Do not cycle the circuit breakers yourself to force a power-cycle reset
- Who:
- You (the homeowner or user), by leaving the electrical cabinet breakers in their normal state.
- How:
- Check visually that the circuit breakers labelled with 'Do NOT turn OFF the circuit breaker' stickers are ON, and do not switch them OFF and ON to clear U2-07.
- Result that matters:
- Keeping the unit's R290 leak detection and anti-blockage routines active while avoiding unmonitored power cycles on a faulted converter.
- If someone already cycled the power and U2-07 returned after the 5 minutes initialization period, that confirms the converter error is persistent and rules out a transient latch.
- If the breakers have not been cycled, that leaves the system protected until the installer can inspect the supply and perform a controlled power cycle.
- Evidence to keep:
- Record whether any power interruption or breaker reset occurred and how many minutes passed before U2-07 returned.
Daikin warns: after commissioning, do NOT turn OFF the circuit breakers to the units so that the protection remains activated.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Verify backup heating status in [5.23] Emergency selection
- Who:
- You, via the indoor unit touchscreen menu.
- How:
- Check [5.23] Settings > Emergency selection (or the [5.30] Emergency acknowledgement pop-up on the screen) to see if the backup heater is allowed to provide space heating and hot water while the heat pump is stopped.
- Result that matters:
- Knowing whether the indoor unit's electrical heater will maintain room warmth and domestic hot water until service arrives.
- If Emergency selection is Automatic or you acknowledge the [5.30] pop-up, that confirms the electrical heater takes over space heating and DHW according to the configured mode.
- If Emergency selection is set to Manual without acknowledgement, that indicates space heating and DHW remain off (while room frost protection and water pipe freeze prevention stay active).
- Evidence to keep:
- Keep a photo of the [5.23] Emergency selection screen and the home screen status icons.
Do not change installer configuration wizard settings in [10] to force heater output; use only the user-level [5.23] or [5.30] emergency controls.
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 U2-07
- code erreur Daikin Altherma U2-07
- codice U2-07 pompa di calore Daikin
- código U2-07 bomba de calor Daikin
- Daikin Altherma error U2-07
- Daikin Altherma Fehler U2-07
- Daikin heat pump code U2-07
- Daikin U2-07
- Daikin Wärmepumpe Fehlercode U2-07
- défaut U2-07 pompe à chaleur Daikin
- error Daikin Altherma U2-07
- errore Daikin Altherma U2-07
What it means
In Daikin installer reference guide 4PEN773391-1C (Chapter 14, section 14.4.4, page 214), code U2-07 is classified as a Supply voltage error with the trigger Converter error. The controller stops the heat pump from operating and lists Power cycle as the reset method. Because Daikin instructs users not to turn off the unit circuit breakers after commissioning (to keep R290 safety protections active) and states that the problem must be understood before resetting an error code, a technician must verify whether a supply disturbance or an outdoor unit converter/PCB fault caused U2-07; the code alone does not prove the converter hardware is defective.
Warnings and stop conditions
- Highsource verified
Never repeatedly turn the heat pump circuit breakers OFF and ON to clear U2-07: turning off the breakers disables the R290 leak detection protection and does not fix an underlying converter or supply voltage fault.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- Highsource verified
Before inspecting the switch box or converter wiring, the technician must disconnect the unit from the mains by turning off the respective circuit breaker to prevent electrocution.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Symptoms and causes
Probable causes · in order
- Power supply disturbance or voltage anomaly affecting the outdoor converterCommon
A grid disturbance, voltage out of specification, or loose field wiring connection disrupts the outdoor unit converter stage and latches U2-07 until a power cycle is performed.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Persistent converter fault on the outdoor unit power electronicsPossible
If U2-07 reappears after a controlled power cycle when supply voltage and wiring are verified normal, the converter circuit inside the outdoor unit has an internal hardware fault.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does U2-07 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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