- Heat pumps
- Air-to-water heat pump
U3-00
Daikin Altherma 4 H F U3-00: Underfloor heating screed dryout function not completed correctly
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
U3-00 means “Underfloor heating screed dryout function not completed correctly” on the scoped Altherma 4 H F family. Daikin records this trigger: Underfloor heating screed dry-out is interupted. 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
- Keep the check outside the casing
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measured handoff for U3-00
What a technician must be able to justify
A technician is coming
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 U3-00
What they doGive the technician U3-00, both model numbers, the source trigger “Underfloor heating screed dry-out is interupted”, the effect “Unit will stop operating”, reset result and recurrence conditions. They should follow Daikin's exact controller decision 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.
Checks and evidence, step by step
Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
- 1
Preserve the diagnostic state
No special tools
Procedure
Photograph U3-00 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
- 2
Use the displayed reset path once
No special tools
Procedure
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
- 3
Keep the check outside the casing
No special tools
Procedure
Use only normal controls and user-accessible observations. Do not remove covers, bypass a safety device or replace a part from the code alone.
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
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 U3-00
- code erreur Daikin Altherma U3-00
- codice U3-00 pompa di calore Daikin
- código U3-00 bomba de calor Daikin
- Daikin Altherma error U3-00
- Daikin Altherma Fehler U3-00
- Daikin heat pump code U3-00
- Daikin U3-00
- Daikin Wärmepumpe Fehlercode U3-00
- défaut U3-00 pompe à chaleur Daikin
- error Daikin Altherma U3-00
- errore Daikin Altherma U3-00
What it means
In guide 4P773391-1C (2026.02), Daikin assigns U3-00 to “Underfloor heating screed dryout function not completed correctly”. The documented trigger is “Underfloor heating screed dry-out is interupted” 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
- Highsource 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 “Underfloor heating screed dryout function not completed correctly” and gives this exact trigger: Underfloor heating screed dry-out is interupted.
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 U3-00 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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