UJ-26 on a Daikin Altherma: AF caution
Short answer
On a Daikin heat pump, UJ-26 means: AF caution. The heat pump keeps running. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: AF caution.
Part involved: inter-unit communication / PCB combination.
When it shows: Active filter operation caution. NOTICE the water volume and flow rate" NOTICE NOTICE INFORMATION ▪ stuck BSH relay. ▪ displayed. ▪ During because the disinfection. INFORMATION consumption control. INFORMATION certified technician. NOTICE INFORMATION ▪ "2 ▪ "3.1 15.1.1 Use the service ports (a)(b) to recover refrigerant.
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Warning |
| Engineer needed? | Yes |
The heat pump keeps running.
Resetting itself: yes.
Manual reset: Automatic To check If error EC-00 is displayed, indicating overheating of the tank, it could be due to a (weekly), the error code AH-00 is displayed requested temperature required for tank MUST be treated at a specialised treatment facility for reuse, recycling and recovery. [4 22] To recover refrigerant............................................................................................................................................................224 To manually open the electronic expansion valves..............................................................................................227.
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.
- 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
- See Daikin service manual for this generation (not public).
Who to ask for: Heat pump installer (Daikin-trained).
Certification: None specific; MCS-certified installer recommended.
What you might notice
What owners and engineers report
13 owner and engineer reports mention this.
- No heating on the Altherma: 7 reports
- Controller / thermostat problem on the Altherma: 6 reports
Sources
- Installer reference guide Daikin Altherma 3 H MT F EPRA08-12E + ETVH12UE6V (4P644482-1) ↗ · 4P644482-1 · page 258 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026