E428 on a Samsung heat pump: COMP down by Compression Ratio control Error
Short answer
On a Samsung heat pump, E428 means: COMP down by Compression Ratio control Error. 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: COMP down by Compression Ratio control Error.
Part involved: Compressor / refrigerant cycle protection.
When it shows: Unit self-diagnosis: COMP down by Compression Ratio control Error.
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 circuit pressures (compression ratio protection).
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 circuit pressures (compression ratio protection). 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; R290 (A3 flammable refrigerant) competence.
Certification: F-gas certification (UK F-gas Regulation; e.g. City & Guilds 2079 Cat I); R290/flammable refrigerant handling training (e.g. hydrocarbon refrigerant course).
What you might notice
Sources
- EHS R290 Mono Outdoor Unit Installation Manual AE***CXYD** (EU) DB68-12496A-03 ↗ · DB68-12496A-03 · page p.24 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026