- Heat pumps
- Air-to-water heat pump
80-03
Daikin Altherma 4 H F 80-03: main zone water sensor fault
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
High
Quick answer
Code 80-03 on a Daikin Altherma 4 H F means the entering water temperature thermistor for the main zone is malfunctioning on a bizone unit, while the unit keeps running (automatic reset). Check [11] Malfunction history and note if it is a bizone system before calling your installer.
Safety first
Stop and check this first
- Do not open the indoor unit or bizone switch box cover; internal electrical inspections must be carried out by a qualified technician with all power supplies switched off.
- Never disconnect or substitute a thermistor with a fixed resistor to silence 80-03; Daikin requires operating the unit with all thermistors and pressure sensors connected and functional.
Safe checks you can perform
- Confirm whether your installation is a bizone system and inspect [11] Malfunction history
- Review sensor readings in [6.3] Sensors and compare main-zone comfort behaviour
- Record unit model numbers and installer details in [6.2] Dealer information without cycling power
Leave these tasks to a qualified professional
- Do not attempt this professional task: Inspect the bizone sensor harness, pipe mounting pocket, and PCB input terminal
- Do not attempt this professional task: Measure the main-zone entering water thermistor resistance on the bizone circuit
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.
Inspect the bizone sensor harness, pipe mounting pocket, and PCB input terminal
What they doThe technician must inspect the bizone thermistor cable run, verify that the sensor bulb is seated firmly with proper thermal contact on the main-zone return pipe, clean and reseat the board connector, and verify that 80-03 clears automatically once a valid signal is restored.
They must show youthe physical mounting of the main-zone return thermistor and the live temperature reading in the controller after reconnecting the circuit.
In writingconfirmation of harness continuity, connector inspection findings, and the stable main-zone entering water temperature reading after repair.
Measure the main-zone entering water thermistor resistance on the bizone circuit
What they doAn authorised Daikin technician must isolate the power supply, disconnect the main-zone entering water thermistor plug, measure its resistance with a calibrated multimeter at a known pipe temperature, and compare the reading against the Daikin service manual resistance table.
They must show youthe ohm reading of the disconnected main-zone entering water thermistor alongside the reference temperature measured at the pipe.
In writingmeasured resistance in ohms, the reference temperature, and whether the probe met or failed Daikin's thermistor table.
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.
Confirm whether your installation is a bizone system and inspect [11] Malfunction history
- Who:
- The homeowner or system operator using the indoor user interface.
- How:
- Tap the 80-03 notification on the screen to view the long description, then set the user permission level to advanced end user and open [11]: Malfunction history to see when 80-03 occurred.
- Result that matters:
- Whether the system uses two heating zones (bizone) and whether 80-03 clears and returns automatically during main-zone heating demand.
- If 80-03 appears repeatedly whenever the main zone calls for heating on a bizone system, that points to an active fault in the main-zone entering water thermistor circuit.
- If 80-03 logged once and cleared automatically with stable main-zone heating afterward, that suggests a transient connection or contact disturbance that still warrants logging for the next service visit.
- Evidence to keep:
- A photo of the 80-03 long description and the dated entries in [11] Malfunction history.
Use only the user interface menus; do not remove casing panels or touch bizone wiring.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Review sensor readings in [6.3] Sensors and compare main-zone comfort behaviour
- Who:
- The homeowner or operator checking live information on the indoor controller.
- How:
- Navigate to [6.3]: Information > Sensors on the user interface and observe the reported water temperatures while noting whether the main heating zone warms normally.
- Result that matters:
- Whether the displayed water temperature readings look plausible or jump erratically while the unit continues operating.
- If the sensor readout is frozen, extreme, or erratic while the unit runs, that confirms the controller is receiving an abnormal main-zone entering water signal.
- If the readings in [6.3] Sensors look normal and the code has already auto-reset, that indicates an intermittent harness contact or thermal-seating issue rather than a permanently open probe.
- Evidence to keep:
- A photo or written note of the values displayed in [6.3] Sensors alongside the active operating mode.
Do not unplug, heat, cool, or bridge any thermistor lead to alter the reading on the screen.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Record unit model numbers and installer details in [6.2] Dealer information without cycling power
- Who:
- The homeowner preparing the service handoff.
- How:
- Because Daikin classifies 80-03 as automatic reset and the unit continues operation, leave the main power supply ON and open [6.2]: Information > Dealer information to note the service contact.
- Result that matters:
- The unit continues space heating and domestic hot water operation while preserving the diagnostic trail.
- If the unit continues heating the building with 80-03 present, that confirms the documented operating effect for a bizone main-zone return thermistor abnormality.
- If space heating stops completely or another fault code appears alongside 80-03, that points to an additional malfunction beyond 80-03 that must be reported to the technician.
- Evidence to keep:
- Indoor and outdoor model numbers, bizone kit details if visible externally, and the contact details from [6.2] Dealer information.
After commissioning, do not turn OFF the power supply to clear an automatic-reset thermistor error.
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 80-03
- code erreur Daikin Altherma 80-03
- codice 80-03 pompa di calore Daikin
- código 80-03 bomba de calor Daikin
- Daikin 80-03
- Daikin Altherma error 80-03
- Daikin Altherma Fehler 80-03
- Daikin heat pump code 80-03
- Daikin Wärmepumpe Fehlercode 80-03
- défaut 80-03 pompe à chaleur Daikin
- error Daikin Altherma 80-03
- errore Daikin Altherma 80-03
What it means
In the Daikin Altherma 4 H F installer reference guide (4PEN773391-1C), code 80-03 is defined as Entering water temperature thermistor main zone abnormality when the entering water thermistor for the main zone is malfunctioning. Daikin explicitly notes that this error exists only for a bizone unit; the heat pump continues operation and the reset classification is automatic. The code alone does not prove the thermistor probe itself has failed, because a loose plug or damaged lead on the bizone kit wiring harness, poor thermal contact on the main-zone return pipe, or a PCB sensing input fault can produce the same reading.
Warnings and stop conditions
- Mediumsource verified
Do not open the indoor unit or bizone switch box cover; internal electrical inspections must be carried out by a qualified technician with all power supplies switched off.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
- Mediumsource verified
Never disconnect or substitute a thermistor with a fixed resistor to silence 80-03; Daikin requires operating the unit with all thermistors and pressure sensors connected and functional.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Symptoms and causes
Probable causes · in order
- Out-of-range resistance or internal short/open in the main-zone entering water thermistorCommon
The thermistor monitoring return water temperature from the main space-heating zone on a bizone installation has drifted outside its valid resistance curve, folded into an open circuit, or shorted internally.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Loose connector, moisture ingress, or damaged cable on the bizone thermistor harnessCommon
Because 80-03 applies exclusively to a bizone unit, an unseated connector, pinched sensor wire, or damp plug between the main-zone return thermistor and the control board can interrupt the temperature signal.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Dislodged thermistor bulb or degraded thermal contact on the main-zone return pipePossible
If the sensor bulb slips out of its pocket or clip on the main-zone return header, the controller receives implausible return water temperature readings during zone circulation.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Electronic sensing channel fault on the PCB reading the main-zone return thermistorLess common
When the main-zone entering water thermistor measures within Daikin's resistance-temperature specification and the harness continuity is intact, the analog input circuit on the board can be defective.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does 80-03 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
Was this entry useful?