E3-00 on a Daikin Altherma: OU: Actuation of high pressure switch (HPS)
Short answer
On a Daikin heat pump, E3-00 means: OU: Actuation of high pressure switch (HPS). The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: OU: Actuation of high pressure switch (HPS).
Part involved: refrigerant circuit / pressure protection.
When it shows: High pressure switch opens due to measured pressure above high pressure switch operating point. High pressure control (measured pressure just below high pressure switch operating point) occurs 16 times within 300 minutes.
Likely causes:
- Closed stop valve in the refrigerant circuit.; Faulty refrigerant pressure sensor.; Faulty high pressure switch.; Faulty main PCB.; Refrigerant overcharge.; Non‑condensables and/or humidity in the refrigerant circuit.; Clogged refrigerant circuit.; Faulty outdoor unit fan motor.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Safety lockout |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: Manual reset via user interface.
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.
- 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).
- 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
- Check that all stop valves of the refrigerant circuit are open. . ; Perform a check of the refrigerant pressure sensor. . ; Perform a check of the high pressure switch. . ; Perform a check of the main PCB. . ; Check if the refrigerant circuit is correctly charged. . ; Check for the presence of non‑condensables and/or humidity in the refrigerant circuit. . ; Check if the refrigerant circuit is clogged. . ; Perform a check of the outdoor unit fan motor. . ; | Troubleshooting.
Who to ask for: F-gas certified heat pump engineer (Daikin-trained installer / Stand By Me partner).
Certification: UK F-gas certification (Category I) for refrigerant circuit work; R-290 (Altherma 4) also needs flammable-refrigerant/hydrocarbon competence.
What you might notice
What owners and engineers report
11 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
Sources
- Service manual Daikin Altherma 3 M EBLA/EDLA04~08E (ESIE22-09) ↗ · ESIE22-09 · page 42 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026