Error F.733 indicates a high-pressure safety circuit activation on the refrigeration loop. The discharge pressure sensor or high-pressure switch (P_HD) detected refrigerant pressure exceeding 41.5 bar (or equivalent R290 design safety threshold), triggering an immediate inverter compressor lockout to prevent mechanical burst.

⏱ 45-60 Mins Troubleshoot →

CODE F.733 aroTHERM plus VWL Critical

Inverter Compressor Synchronization Failure

Error F.733 indicates that the inverter driver board lost rotor position synchronization with the brushless DC (BLDC) scroll compressor motor. The inverter microprocessor detects a phase-angle mismatch, excessive back-EMF distortion, or sudden loss of feedback during ramp-up, tripping hardware protection to prevent catastrophic IGBT bridge or motor winding destruction.

⏱ 45-60 Mins Troubleshoot →

CODE F.733 aroTHERM plus Critical

EEV EEB Stall High Pressure

Error F.733 indicates a high-pressure refrigeration circuit trip caused by a mechanical stall or electrical failure of Electronic Expansion Valve B (EEB / injection valve), causing rapid head pressure buildup.

⏱ 45-75 Mins Troubleshoot →

CODE F.733 aroTHERM plus VWL 125/6 A Critical

Compressor Motor Phase Disconnection

The inverter PCB detects a loss of current feedback or an open circuit across one of the three motor drive phases (U, V, W) supplying the hermetic scroll compressor, triggering an immediate shutdown to prevent IPM driver destruction and unbalance stress.

⏱ 45-60 Mins Troubleshoot →

CODE F.733 aroTHERM plus VWL (R290) Critical

Inverter Compressor Driver Board Fault

Fault F.733 denotes an inverter communication or hardware trip on the compressor driver board (power electronics). The system shuts down compressor operation to protect the hermetic scroll compressor and IPM from phase failure, overcurrent, or DC-bus voltage instability.

⏱ 45-60 Mins Troubleshoot →

CODE F.733 aroTHERM plus VWL 125/6 High

Inverter Compressor Communication Fault

Error F.733 indicates a critical serial communication failure between the outdoor unit main PCB and the compressor inverter driver board. The safety control loop aborts compressor operation to prevent phase loss, DC bus overcurrent, or uncontrolled motor drive states.

⏱ 30-60 Mins Troubleshoot →

CODE F.733 aroTHERM plus VWL 75/6 A Critical

High Pressure Switch Open Circuit

The inverter controller detected an open circuit condition on the high-pressure safety switch (HP switch) input circuit. This is a failsafe lock protecting the hermetic compressor from excessive discharge line pressures, typically caused by a disconnected harness, failed switch contact, or an actual overpressure event.

⏱ 30-45 Mins Troubleshoot →

CODE F.733 aroTHERM Split Critical

Compressor Inverter Module Fault

Fault F.733 indicates a hardware or commutation failure within the outdoor unit compressor inverter drive. The outdoor unit PCB has detected an overcurrent, phase imbalance, or internal power module (IPM) failure on the variable-speed compressor circuit, triggering a protective safety shutdown.

⏱ 30-45 Mins Troubleshoot →

CODE F.28 ecoTEC plus High

Ignition and Flame Lockout Failure

The automatic burner control unit detected an ignition failure during initial start-up. After three ignition attempts, no stable flame ionization current (less than 1.5 microamps DC) was established, triggering a safety shutoff of the gas valve solenoids.

⏱ 30-45 Mins Troubleshoot →

CODE F.28 ecoTEC plus High

Ignition Failure / No Gas Supply

Fault code F.28 on Vaillant boilers signifies that the unit attempted 3 to 5 ignition cycles but failed to establish or detect a stable flame, causing a safety lockout.

⏱ 15-30 Mins Troubleshoot →