- Heat pumps
- Air-to-water heat pump
8H-03
Daikin Altherma 4 H F 8H-03: Overheating of the space heating water circuit thermostat
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
High
Quick answer
8H-03 means “Overheating of the space heating water circuit thermostat” on the scoped Altherma 4 H F family. Daikin records this trigger: The thermostat of the space heating water circuit has tripped. Effect: Pump will stop running. The table marks the reset as automatic.
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
- Let the automatic reset logic decide
- Do not substitute a sensor diagnosis
Leave these tasks to a qualified professional
- Do not attempt this professional task: Measured handoff for 8H-03
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 8H-03
What they doGive the technician 8H-03, both model numbers, the source trigger “The thermostat of the space heating water circuit has tripped”, the effect “Pump will stop running”, 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 8H-03 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
Let the automatic reset logic decide
Daikin marks this code as automatic reset. Do not cycle breakers or force repeated acknowledgements. Record whether the controller clears it and the exact operating state in which it returns.
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 8H-03
- code erreur Daikin Altherma 8H-03
- codice 8H-03 pompa di calore Daikin
- código 8H-03 bomba de calor Daikin
- Daikin 8H-03
- Daikin Altherma error 8H-03
- Daikin Altherma Fehler 8H-03
- Daikin heat pump code 8H-03
- Daikin Wärmepumpe Fehlercode 8H-03
- défaut 8H-03 pompe à chaleur Daikin
- error Daikin Altherma 8H-03
- errore Daikin Altherma 8H-03
What it means
In guide 4P773391-1C (2026.02), Daikin assigns 8H-03 to “Overheating of the space heating water circuit thermostat”. The documented trigger is “The thermostat of the space heating water circuit has tripped” and the operating effect is “Pump will stop running”. 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 “Overheating of the space heating water circuit thermostat” and gives this exact trigger: The thermostat of the space heating water circuit has tripped.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- What the unit does nextConfirmed
Documented effect: Pump will stop running. Reset classification: Automatic. A cleared display is not proof of repair.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does 8H-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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