F3 on a Daikin heat pump: Code shown on the remote controller for the installation error(s): Stop valve left closed; insufficient refrigerant (Flex outdoor installation manual, test-operation table)
Short answer
On a Daikin heat pump, F3 means: Code shown on the remote controller for the installation error(s): Stop valve left closed; insufficient refrigerant (Flex outdoor installation manual, test-operation table). The manual does not say whether the heat pump stops. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 3 sources
What it means
On the Altherma Flex Type
The manual says: Code shown on the remote controller for the installation error(s): Stop valve left closed; insufficient refrigerant (Flex outdoor installation manual, test-operation table).
Part involved: refrigerant circuit / pressure protection.
When it shows: Detected during test operation / normal operation after installation errors listed.
Likely causes:
- Stop valve left closed; insufficient refrigerant.
On the Altherma HT (high temperature split)
The manual says: Abnormal discharge pipe temperature.
Part involved: refrigerant circuit / pressure protection.
When it shows: When the discharge pipe temperature rises to an abnormally high level When the discharge pipe temperature rises suddenly.
Likely causes:
- Faulty discharge pipe temperature sensor; Faulty connection of dischar ge pipe temperature sensor; Faulty outdoor unit PC board; Faulty discharge pipe temperature sensor (R6T); Faulty indoor unit PC board.
On the Altherma LT (low temperature split)
The manual says: Discharge pipe temperature control.
Part involved: refrigerant circuit / pressure protection.
When it shows: ■ If a stop takes place 6 times successively due to abnormal discharge pipe temperature, the system will be shut down. ■ If the temperature being detected by the discharge pipe thermistor rises above °C, the compressor will stop. (The error is cleared when the temperature has dropped below °C. ■ The error counter will reset itself if this or any other error does not occur during the following 60-minute compressor running time (total time) | If a stop takes place 6 times successively due to abnormal discharge pipe temperature, the system will be shut down. If the temperature being detected by the discharge pipe thermistor rises above °C, the 3 3 compressor will stop. (The error is cleared when the temperature has dropped below °C. 71 class 120 107 The error counter will reset itself if this or any other error does not occur during the following 60-minute compressor running time (total time).
Likely causes:
- Refrigerant shortage; Four way valve malfunctioning; Discharge pipe thermistor defective (heat exchanger or outdoor temperature thermistor defective); Outdoor unit PCB defective; Water mixed in the local piping; Electronic expansion valve defective; Stop valve defective 006~008 class 120 107; Discharge pipe thermistor defective; (heat exchanger or outdoor temperature thermistor defective); Stop valve defective.
Is it safe?
On the Altherma Flex Type
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
Manual reset: After correcting the abnormality press BS3 RETURN on the outdoor PCB to reset and repeat the test operation (installer only).
On the Altherma HT (high temperature split)
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
Resetting itself: unknown.
On the Altherma LT (low temperature split)
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: unknown.
Manual reset: Reset via the remote controller (Inspection/Test button) after the cause is fixed; some codes need a manual reset of the remote-controller memory (service manual section 1.4).
What you can check
- Read the full error code shown on the user interface 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).
What the engineer will check
On the Altherma Flex Type
- Installer remedial action per manual: open stop valves; correct phase sequence; check power wiring; check piping/wiring consistency; correct refrigerant charge by recalculation; repeat test operation within -20~35 C.
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.
On the Altherma HT (high temperature split)
- Follow the service-manual troubleshooting flow chart for this code: check faulty discharge pipe temperature sensor; check faulty connection of dischar ge pipe temperature sensor; check faulty outdoor unit PC board; check faulty discharge pipe temperature sensor (R6T); check faulty indoor unit PC board.
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.
On the Altherma LT (low temperature split)
- Follow the service-manual troubleshooting flow chart for this code: check refrigerant shortage; check four way valve malfunctioning; check discharge pipe thermistor defective (heat exchanger or outdoor temperature thermistor defective); check outdoor unit PCB defective; check water mixed in the local piping; check electronic expansion valve defective.
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
1 owner and engineer report mentions this.
- No heating on the Altherma LT (low temperature split): 1 report
Sources
- Installation manual Daikin Altherma Flex EMRQ8-16AAY1 (4PWEN61262-1B) ↗ · 4PWEN61262-1B · page 32 (printed 29) · Reviewed 23 September 2026
- Service Manual Daikin ALTHERMA HT ERSQ/ERRQ 011-016 AA V1/Y1 + EKHBRD (ESIE09-08C) ↗ · ESIE09-08C · page 178 · Reviewed 23 September 2026
- Service Manual ALTHERMA ERHQ006~008BAV3 / ERLQ006~008BAV3(9) / EKHBH(X)008BA (ESIE10-02) ↗ · ESIE10-02 · page 167 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026