OU-67 on a Fujitsu WATERSTAGE split: Outdoor unit power short interruption error (protective operation)

What it means

The manual says: Outdoor unit power short interruption error (protective operation).

Part involved: outdoor unit PCB/refrigerant circuit.

Likely causes:

• Momentary power interruption.

Is it safe?

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. Check both the hydraulic unit and outdoor unit supplies are on (breakers/isolators) - a recent power cut can cause this.

What the engineer will check

• Per SHP maintenance manual 'Clear' procedure: Momentary power interruption. 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

• Hydraulic unit shows fault 370 ('thermodynamic source'); heat pump heating stops (electric backup may run if emergency mode set to automatic)

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; 1768-3 p.69 · Reviewed 23 September 2026

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

Reviewed: 23 September 2026