- Heat pumps
- Air-to-water heat pump
81-07
Daikin Altherma 4 H F 81-07: tank valve water sensor fault
Risk level
Medium
Proceed carefully and stop if the check is unclear.
Urgency
High
Quick answer
Code 81-07 on a Daikin Altherma 4 H F means the exit water temperature thermistor after the tank valve is malfunctioning, while the unit continues operating with automatic reset. Check [11] Malfunction history and [6.3] Sensors on the indoor controller before contacting your installer.
Safety first
Stop and check this first
- Do not open the indoor unit casing or switch box cover; internal hydronic and electrical inspections around the tank valve and PCB require a qualified technician after full power isolation.
- Never operate the heat pump with the post-tank-valve thermistor unplugged or bridged with a fixed resistor; Daikin mandates operating the unit with all thermistors and pressure sensors connected.
Safe checks you can perform
- Inspect the 81-07 long description and event timestamps in [11] Malfunction history
- Check live readings in [6.3] Sensors and verify continued heating and hot water operation
- Collect dealer contact details in [6.2] Dealer information while keeping the power supply ON
Leave these tasks to a qualified professional
- Do not attempt this professional task: Disconnect power safely and measure the resistance of the exit water thermistor after the tank valve
- Do not attempt this professional task: Inspect the sensor clip and wiring near the tank valve and verify automatic reset of 81-07
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.
Disconnect power safely and measure the resistance of the exit water thermistor after the tank valve
What they doAn authorised Daikin technician must switch off all power supplies for more than 10 minutes, verify less than 50 V DC inside the switch box, unplug the exit water temperature thermistor located after the tank valve, and test its resistance with a multimeter against the service manual specification.
They must show youthe multimeter ohm reading of the disconnected thermistor probe and the reference temperature measured on the pipe downstream of the tank valve.
In writingmeasured thermistor resistance in ohms, the reference pipe temperature, and whether the sensor passed or failed the Daikin service curve.
Inspect the sensor clip and wiring near the tank valve and verify automatic reset of 81-07
What they doThe technician must inspect the thermistor cable routing past the motorized tank valve for chafing or moisture, ensure the sensor bulb is firmly clipped to the outlet pipe after the tank valve, reconnect or replace the thermistor, and verify that 81-07 resets automatically.
They must show youthe secured thermistor mounting downstream of the tank valve and the cleared status on the indoor user interface.
In writingconfirmation of harness continuity, proper sensor seating after the tank valve, and stable water temperature readings in [6.3] Sensors with 81-07 cleared.
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.
Inspect the 81-07 long description and event timestamps in [11] Malfunction history
- Who:
- The homeowner or system operator working at the indoor user interface.
- How:
- Select the 81-07 notification on the home screen to read the full text, then set the user permission level to advanced end user and open [11]: Malfunction history.
- Result that matters:
- Whether 81-07 stays latched continuously or appears and clears automatically when the unit switches between domestic hot water tank heating and space heating.
- If 81-07 appears specifically during transitions of the tank valve between hot water and space heating, that points to a thermal-seating issue or a harness lead flexed near the valve.
- If 81-07 remains active at all times regardless of valve position, that indicates a continuous open or short circuit in the thermistor after the tank valve or its board plug.
- Evidence to keep:
- A photo of the 81-07 long description screen and the history log in [11] Malfunction history.
Operate only the external user interface; do not remove indoor unit panels to inspect the tank valve or sensors.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Check live readings in [6.3] Sensors and verify continued heating and hot water operation
- Who:
- The homeowner or operator checking the indoor user interface.
- How:
- Navigate to [6.3]: Information > Sensors to observe the reported water temperatures and verify whether space heating and domestic hot water continue operating.
- Result that matters:
- Whether the unit continues operation as stated in the troubleshooting table and whether sensor values in [6.3] Sensors look abnormal.
- If the unit continues running while 81-07 is active, that confirms the documented operating effect (Unit will continue operation) for this automatic-reset thermistor fault.
- If domestic hot water or space heating performance degrades noticeably or additional error codes appear, that suggests the controller's fallback control is affected or a second fault is present.
- Evidence to keep:
- A photo of the values in [6.3] Sensors and notes on hot water tank and space heating behaviour.
Do not unplug, heat, cool, or bypass any internal thermistor to alter the controller reading.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C · Daikin Altherma 4 H F+W+ECH2O operation manual 4PEN773378-1C
Collect dealer contact details in [6.2] Dealer information while keeping the power supply ON
- Who:
- The homeowner preparing to contact the installer.
- How:
- Open [6.2]: Information > Dealer information on the user interface to note the service phone number and record the indoor unit model code (such as EPVX or EPBX with integrated tank valve).
- Result that matters:
- The installer receives the exact model and code 81-07 while the unit continues operating safely.
- If you give the technician code 81-07 and the indoor model code in advance, that confirms they can bring the matching exit water thermistor located after the tank valve.
- If 81-07 started right after plumbing or valve maintenance inside the indoor unit, that points to a disturbed thermistor plug or clip near the tank valve.
- Evidence to keep:
- Written record of the indoor and outdoor model numbers and the contact details from [6.2] Dealer information.
After commissioning, do not turn OFF the power supply to clear an automatic-reset code.
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 81-07
- code erreur Daikin Altherma 81-07
- codice 81-07 pompa di calore Daikin
- código 81-07 bomba de calor Daikin
- Daikin 81-07
- Daikin Altherma error 81-07
- Daikin Altherma Fehler 81-07
- Daikin heat pump code 81-07
- Daikin Wärmepumpe Fehlercode 81-07
- défaut 81-07 pompe à chaleur Daikin
- error Daikin Altherma 81-07
- errore Daikin Altherma 81-07
What it means
In the Daikin Altherma 4 H F installer reference guide (4PEN773391-1C), code 81-07 is assigned to Exit water temperature thermistor after tank valve abnormality when the exit water temperature thermistor downstream of the domestic hot water tank valve is malfunctioning. According to the troubleshooting table, the unit will continue operation and the reset classification is automatic. The code alone does not prove the thermistor probe itself has failed, because a loose harness connector, moisture or chafing on the sensor wire near the motorized tank valve, poor thermal contact on the outlet pipe after the tank valve, or a PCB input fault can trigger the same detection.
Warnings and stop conditions
- Mediumsource verified
Do not open the indoor unit casing or switch box cover; internal hydronic and electrical inspections around the tank valve and PCB require a qualified technician after full power isolation.
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 operate the heat pump with the post-tank-valve thermistor unplugged or bridged with a fixed resistor; Daikin mandates operating the unit with all thermistors and pressure sensors connected.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Symptoms and causes
Probable causes · in order
- Open circuit, short circuit, or resistance drift in the exit water thermistor after the tank valveCommon
The thermistor measuring water temperature downstream of the tank 3-way valve has drifted outside its calibrated resistance curve, failed open, or shorted internally.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Loose connector, pinched lead, or moisture on the thermistor harness near the tank valveCommon
Movement or servicing around the motorized tank valve and internal piping can loosen the thermistor plug on the indoor PCB or damage the sensor cable insulation.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Dislodged thermistor clip or poor thermal contact on the pipe downstream of the tank valvePossible
If the sensor bulb is not seated tightly against the water pipe after the tank valve, the measured exit water temperature lags or diverges during switching between space heating and tank heating.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
- Indoor PCB analog input fault for the post-tank-valve exit water thermistor channelLess common
When the disconnected thermistor meets Daikin's resistance specification and the wiring harness shows intact continuity and insulation, the sensing input on the indoor PCB can be defective.
Evidence: Daikin Altherma 4 H F installer reference guide — 4PEN773391-1C
Virtual technician
Does 81-07 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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