E4 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, E4 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 · 2 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: Actuation of low pressure sensor.
Part involved: thermistor / pressure sensor.
When it shows: Error is generated when the low pressure is dropped under specific pressure. Operating pressure: 0.07MPa.
Likely causes:
- Abnormal drop of low pressure (Lower than 0.07MPa); Defect of low pressure sensor; Defect of outdoor unit PC board (A1P); Stop valve is not opened. ESIE09-08C; Defect control PC board (A4P); Stop valve is not opened. Warning: CAPACITOR SHOCK HAZARD. The capac itors (top surfaces) can hold up to 220V. Use correct precautions when servicing. ESIE09-08C.
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.
What you can check
On the Altherma Flex Type
- 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).
On the Altherma HT (high temperature split)
- Read the full error code shown on the user interface and note it, with the date/time, for your installer.
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 abnormal drop of low pressure (Lower than 0.07MPa); check defect of low pressure sensor; check defect of outdoor unit PC board (A1P); check stop valve is not opened. ESIE09-08C; check defect control PC board (A4P); check stop valve is not opened. Warning: CAPACITOR SHOCK HAZARD. The capac itors (top surfaces) can hold up to 220V. Use correct precautions when servicing. ESIE09-08C.
Who to ask for: Heat pump engineer (Daikin-trained).
Certification: Electrical competence to BS 7671 for sensor/PCB wiring; F-gas if a refrigerant-side sensor must be replaced.
What you might notice
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 166 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026