89-03 on a Daikin heat pump: Heat exchanger freeze-up protection activated during defrost (warning)
Short answer
On a Daikin heat pump, 89-03 means: Heat exchanger freeze-up protection activated during defrost (warning). The heat pump keeps running. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Altherma
The manual says: Heat exchanger freeze-up protection activated during defrost (warning).
Part involved: plate heat exchanger freeze protection.
When it shows: Evaporation temperature is too low during defrost. Outlet water after heat exchanger thermistor <6°C during defrost.
Likely causes:
- Faulty outlet water after heat exchanger thermistor.; Faulty hydro PCB.
On the Altherma 4 H (R-290)
The manual says: Interruption defrost due to low water volume.
Part involved: plate heat exchanger freeze protection.
When it shows: Plate heat exchanger freeze-up protection activated during defrost on the emitter circuit (auto retry).
Is it safe?
On the Altherma
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: yes.
Manual reset: Automatic reset.
On the Altherma 4 H (R-290)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: yes.
Manual reset: Automatic.
What you can check
- Read the full error code and sub-code shown on the user interface (Malfunctioning screen; press the help button for Daikin's long description) and note it, with the date/time, for your installer.
- Check the heating-system water pressure reading on the gauge/display: Daikin operation manuals ask users to check it is above 1 bar. If it is below that, report it to your installer (do not open the unit).
- Look at the outdoor unit from outside: check the air inlet/outlet and fan grille are not blocked by leaves, debris, snow or heavy ice build-up (do not remove panels or touch the fan).
- Daikin documents this code as resetting automatically once the condition clears; if it keeps coming back, contact your installer.
- Do NOT bleed radiators while an error/malfunction symbol is displayed: Daikin operation manuals warn refrigerant may have leaked into the water circuit - ventilate and call your installer.
- If heating/hot water has stopped, the operation manual lets the user confirm on the Malfunctioning screen whether the backup/booster heater may take over as emergency heating (much higher running cost) until the installer attends.
What the engineer will check
On the Altherma
- Perform a check of the outlet water after heat exchanger thermistor. . ; Perform a check of the hydro PCB. .
Who to ask for: Heat pump installer / heating engineer.
Certification: None specific for water-side checks; MCS-certified installer recommended.
On the Altherma 4 H (R-290)
- See Daikin service manual for this generation (not public).
Who to ask for: Heat pump installer / heating engineer.
Certification: None specific for water-side checks; MCS-certified installer recommended.
What you might notice
What owners and engineers report
14 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Keeps stopping / cutting out on the Altherma: 2 reports
- No hot water on the Altherma: 2 reports
- Stops working in very cold weather on the Altherma: 2 reports
- Frequent defrosting on the Altherma: 1 report
Sources
- Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 27 · Reviewed 23 September 2026
- Installer reference guide Daikin Altherma 4 H W EPSK/EPSKS + EPBX(U) (4P773390-1C) ↗ · 4P773390-1C · page 204 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026