OU-41 on a Fujitsu WATERSTAGE split: Heat pump capacity signal error (open or short)
Short answer
On a Fujitsu heat pump, OU-41 means: Heat pump capacity signal error (open or short). 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: Heat pump capacity signal error (open or short).
Part involved: outdoor unit PCB/refrigerant circuit.
Likely causes:
- Misconnection; sensor failure; interface PCB failure.
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 error number shown after pressing the Info (i) key on the Waterstage user interface. Check the heat pump breakers/isolators are on. The hydraulic unit shows error 370; the specific code is shown by LED flashes on the hydraulic interface PCB / outdoor PCB, which only an engineer should access.
What the engineer will check
- Per SHP maintenance manual 'Clear' procedure: Misconnection; sensor failure; interface PCB failure. Access outdoor PCB (ERROR LED, press ENTER to read flash count), check connectors, sensor resistances, supply voltage (198-264 V AC 1ph), serial signal (AC 70-130 V between terminals), valves/EEV, refrigerant charge (F-gas), fan motor, compressor windings, IPM/PFC boards.
Who to ask for: Heat pump / refrigeration engineer (manufacturer-trained).
Certification: F-gas certification for refrigerant-circuit work; electrical competence (Part P/18th Edition) for PCB/wiring.
What you might notice
Sources
- Maintenance Document - Air to Water Heat Pump Split single service and integrated DHW type (Super High Power) ↗ · 2105_EN_1 · page SHP SM p.6, p.12 (Clear 4) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026