E903 on a Samsung heat pump: Water outlet (backup heater) temperature sensor error
Short answer
On a Samsung heat pump, E903 means: Water outlet (backup heater) temperature sensor error. 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 · 2 sources
What it means
On the EHS Mono R290 (AE***CXYD*K and pump-integrated AE***CXYB*K)
The manual says: Water outlet (backup heater) temperature sensor error.
Part involved: Water outlet (backup heater) temperature sensor error.
When it shows: Unit self-diagnosis: Water outlet (backup heater) temperature sensor error.
Likely causes:
- Water-side or tank temperature sensor open/short circuit, detached or mis-configured; connector or PCB fault.
- Engineer checks per Samsung service manual: Check sensor connection status, sensor location and sensor resistance against the Samsung resistance table (103 or 204 type); replace sensor or PCB if required.
On the EHS Split Generation 4 (AEX/AEN, 2014)
The manual says: Water outlet temperature sensor error (open/short).
Part involved: Water outlet temperature sensor error (open/short).
When it shows: Unit self-diagnosis: Water outlet temperature sensor error (open/short).
Likely causes:
- Water-side or tank temperature sensor open/short circuit, detached or mis-configured; connector or PCB fault.
- Engineer checks per Samsung service manual: Check sensor connection status, sensor location and sensor resistance against the Samsung resistance table (103 or 204 type); replace sensor or PCB if required.
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; then contact your installer or Samsung service; Samsung manuals do not describe a homeowner reset for this code.
What the engineer will check
- Check sensor connection status, sensor location and sensor resistance against the Samsung resistance table (103 or 204 type); replace sensor or PCB if required. Any work inside casings, on PCBs, wiring, sensors, pumps, valves or refrigerant is engineer-only.
Who to ask for: Heat pump engineer (Samsung-trained).
Certification: Competent electrical worker (BS 7671).
What you might notice
Sources
- Air to Water Heat Pump User manual AE200DN**** / AE160DN**** / MIM-E03FN (2024 ClimateHub / control kit) DB68-12922A-05 ↗ · DB68-12922A-05 · page p.57 · Reviewed 23 September 2026
- Samsung Eco Heating System Service Manual - Outdoor Unit AEX060-160ED*HA / Hydro Unit AEN080/160YD*HA (file RC160MHXGA_SM_E_34513A(1)) ↗ · 34513A(1) · page ManualsLib viewer pp.49, 53 (printed pp.48, 52) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026