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Heat pumps · Error codes · Samsung
E404Samsung

E404 on a Samsung heat pump: Protection of OUTDOOR UINT when it is overload

Short answer

On a Samsung heat pump, E404 means: Protection of OUTDOOR UINT when it is overload. The heat pump stops until the fault clears or is reset. 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 EHS Mono HT Quiet (AE***BXYD*G)

The manual says: Protection of OUTDOOR UINT when it is overload.

Part involved: Compressor / refrigerant cycle protection.

When it shows: Unit self-diagnosis: Protection of OUTDOOR UINT when it is overload.

Likely causes:

  • Compressor stopped by refrigerant-cycle protection (pressure, discharge temperature, overload or compression ratio): e.g. refrigerant under/overcharge, blockage, poor water flow or airflow, sensor fault.
  • Engineer checks per Samsung service manual: Check refrigerant cycle status and compressor start (check same as E461).

On the EHS Mono R32 (AE***RXYD*G)

The manual says: Protection of OUTDOOR UNIT when it is overload (during Safety Start, Normal operation state).

Part involved: Compressor / refrigerant cycle protection.

When it shows: Unit self-diagnosis: Protection of OUTDOOR UNIT when it is overload (during Safety Start, Normal operation state).

Likely causes:

  • Compressor stopped by refrigerant-cycle protection (pressure, discharge temperature, overload or compression ratio): e.g. refrigerant under/overcharge, blockage, poor water flow or airflow, sensor fault.
  • Engineer checks per Samsung service manual: Check refrigerant cycle status and compressor start (check same as E461).

On the EHS Split Generation 4 (AEX/AEN, 2014)

The manual says: Protection of Outdoor Overload when Comp. Stop.

Part involved: Compressor / refrigerant cycle protection.

When it shows: Unit self-diagnosis: Protection of Outdoor Overload when Comp. Stop.

Likely causes:

  • Compressor stopped by refrigerant-cycle protection (pressure, discharge temperature, overload or compression ratio): e.g. refrigerant under/overcharge, blockage, poor water flow or airflow, sensor fault.
  • Engineer checks per Samsung service manual: Check refrigerant cycle status and compressor start (check same as E461).

Is it safe?

Does the heat pump stop?Yes
Engineer needed?Yes

The heat pump stops until the fault clears or is reset.

Resetting itself: unknown.

Manual reset: unknown.

What you can check

  • Note the full error code shown on the controller; check the heat pump breaker/isolator in the consumer unit is ON; check the outdoor unit is not blocked by leaves, debris or snow and air can flow freely; check the heating system pressure gauge reading (typically 1-2 bar when cold; do not top up unless you have been shown how); then contact your installer or Samsung service; Samsung manuals do not describe a homeowner reset for this code.

What the engineer will check

  • Check refrigerant cycle status and compressor start (check same as E461). Any work inside casings, on PCBs, wiring, sensors, pumps, valves or refrigerant is engineer-only.

Who to ask for: F-gas certified refrigeration/heat pump engineer.

Certification: F-gas certification (UK F-gas Regulation; e.g. City & Guilds 2079 Cat I).

What you might notice

What owners and engineers report

13 owner and engineer reports mention this.

  • Intermittent fault on the EHS Mono HT Quiet (AE***BXYD*G): 2 reports
  • Keeps stopping / cutting out on the EHS Mono HT Quiet (AE***BXYD*G): 1 report
  • No heating on the EHS Mono HT Quiet (AE***BXYD*G): 1 report
  • No heating on the EHS Mono R32 (AE***RXYD*G): 6 reports
  • Keeps stopping / cutting out on the EHS Mono R32 (AE***RXYD*G): 2 reports
  • Intermittent fault on the EHS Mono R32 (AE***RXYD*G): 1 report

Sources

A code explains what the controller detected, not a confirmed root cause.

Reviewed: 23 September 2026