- Heat pumps
- Air-to-water heat pump
A0-02
Daikin Altherma 4 H F A0-02: Indoor unit gas sensor detection
Risk level
High
Professional inspection is recommended.
Urgency
Immediate
Quick answer
A0-02 means “Indoor unit gas sensor detection” on the scoped Altherma 4 H F family. Daikin records this trigger: The indoor unit gas sensor has detected a gas leakage. Effect: Unit will stop operating. The table marks the reset as manual.
Safety first
Stop and check this first
- Stop and isolate the installation for smoke, burning smell, sparks, unusual heat, water near electrical parts, suspected refrigerant release or repeated protective trips. Do not open the R290 refrigerant circuit or live electrical compartments.
Safe checks you can perform
- Preserve the diagnostic state
- Use the displayed reset path once
- Do not substitute a sensor diagnosis
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measured handoff for A0-02
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.
Measured handoff for A0-02
What they doGive the technician A0-02, both model numbers, the source trigger “The indoor unit gas sensor has detected a gas leakage”, the effect “Unit will stop operating”, reset result and recurrence conditions. They should follow Daikin's sensor and measured value branch and compare live measurements with the service values before replacing parts.
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.
Preserve the diagnostic state
Photograph A0-02 and the complete display. Record both unit model numbers, operating mode, requested temperatures, weather, system pressure shown to the user and the moment the code appeared.
Stop and isolate the installation for smoke, burning smell, sparks, unusual heat, water near electrical parts, suspected refrigerant release or repeated protective trips. Do not open the R290 refrigerant circuit or live electrical compartments.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Use the displayed reset path once
Daikin marks this code as manual reset. Only when the installation is safe, follow the reset instruction shown by the user interface or the exact user manual once. Do not enter maintenance mode; recurrence ends user troubleshooting.
Stop and isolate the installation for smoke, burning smell, sparks, unusual heat, water near electrical parts, suspected refrigerant release or repeated protective trips. Do not open the R290 refrigerant circuit or live electrical compartments.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Do not substitute a sensor diagnosis
Note the displayed temperatures and whether they are stable or implausible. Do not unplug, bridge, heat, cool or resistance-test any sensor and do not open either unit.
Stop and isolate the installation for smoke, burning smell, sparks, unusual heat, water near electrical parts, suspected refrigerant release or repeated protective trips. Do not open the R290 refrigerant circuit or live electrical compartments.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
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 A0-02
- code erreur Daikin Altherma A0-02
- codice A0-02 pompa di calore Daikin
- código A0-02 bomba de calor Daikin
- Daikin A0-02
- Daikin Altherma error A0-02
- Daikin Altherma Fehler A0-02
- Daikin heat pump code A0-02
- Daikin Wärmepumpe Fehlercode A0-02
- défaut A0-02 pompe à chaleur Daikin
- error Daikin Altherma A0-02
- errore Daikin Altherma A0-02
What it means
In guide 4P773391-1C (2026.02), Daikin assigns A0-02 to “Indoor unit gas sensor detection”. The documented trigger is “The indoor unit gas sensor has detected a gas leakage” and the operating effect is “Unit will stop operating”. This is a precise controller decision for Daikin Altherma 4 H F — EPSK(S)04~14A + EPVX07~14S18+23A; it does not by itself prove which component failed.
Warnings and stop conditions
- Criticalsource verified
Stop and isolate the installation for smoke, burning smell, sparks, unusual heat, water near electrical parts, suspected refrigerant release or repeated protective trips. Do not open the R290 refrigerant circuit or live electrical compartments.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Symptoms and causes
Probable causes · in order
- What the controller establishedConfirmed
Daikin's table defines the condition as “Indoor unit gas sensor detection” and gives this exact trigger: The indoor unit gas sensor has detected a gas leakage.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- What the unit does nextConfirmed
Documented effect: Unit will stop operating. Reset classification: Manual. A cleared display is not proof of repair.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does A0-02 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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