Error L5 indicates the outdoor inverter PCB detected instantaneous hardware overcurrent across the compressor drive circuit (IPM). This protection trips when current draw exceeds safe thresholds, caused by compressor winding failure, mechanical seizure, or shorted IGBT switches.

⏱ 45-60 Mins Troubleshoot →

CODE U4-01 Altherma 3 H HT Critical

Outdoor-Indoor Transmission Failure

Error U4-01 designates a serial communication loss between the outdoor hydro/inverter inverter PCB and the indoor hydro unit PCB. The system trips to protect the compressor from unmonitored operational states.

⏱ 30-60 Mins Troubleshoot →

CODE 7H-01 Altherma 3 H HT Critical

Water Flow Switch Interlock Failure

Error 7H-01 triggers when the hydro module Main PCB detects that the water flow switch contact remains open during circulation pump operation (interlock opened) or closed when the pump is idle, indicating insufficient hydronic flow (<12 L/min) or a defective flow sensor circuit.

⏱ 30-45 Mins Troubleshoot →

CODE 7H-01 Altherma 3 Critical

Abnormal Water Flow Vortex Lockout

Error 7H-01 triggers when the hydronic vortex flow sensor detects a flow rate below the operational threshold (typically < 10-12 L/min depending on capacity) or inconsistent pulse frequency during pump operation, forcing a protective safety lockout to prevent heat exchanger freezing or thermal stress.

⏱ 30-45 Mins Troubleshoot →

CODE L5 Altherma 3 R MT Critical

Inverter Compressor Instantaneous Overcurrent

Error L5 indicates the inverter PCB hardware protection detected an instantaneous peak overcurrent through the compressor drive circuit (IPM output), triggered by a seized compressor scroll, shorted motor windings, or shorted power transistors.

⏱ 45-60 Mins Troubleshoot →

CODE 7H Altherma 3 Critical

Water Flow Rate Failure

Error 7H indicates an abnormal water flow rate detected during circulation pump operation. The hydrobox safety logic halts the heat pump cycle when water flow drops below critical operating thresholds (typically < 10-12 L/min) detected by the vortex flow sensor (VFS) to prevent primary plate heat exchanger freezing or thermal runaway.

⏱ 30-45 Mins Troubleshoot →

CODE 7H-01 Altherma 3 M Monobloc Series Critical

Water Flow Rate Abnormality

The hydro PCB registered water flow below the minimum operating safety threshold (typically < 10-12 L/min) via the vortex flow sensor (B1L) during circulation pump operation. The unit triggers an emergency safety shutdown to protect the plate heat exchanger from freezing or thermal shock.

⏱ 30-45 Mins Troubleshoot →

CODE U4 Altherma 3 Series Critical

Indoor Outdoor Communication Failure

Error U4 indicates a critical loss of serial data transmission between the indoor hydro-box and outdoor inverter unit. This triggers a safety lockout, often freezing PCB logic routines due to power phase sync loss, noise coupling, or hardware transceiver failure.

⏱ 30-45 Mins Troubleshoot →

CODE L5 Altherma 3 H HT Critical

Inverter Instantaneous Overcurrent Fault

Error L5 indicates that the outdoor inverter printed circuit board (PCB) detected an instantaneous overcurrent trip on the compressor drive circuit via the current transformer (CT) or shunt resistors. The IPM shut down operation to prevent catastrophic semiconductor and compressor failure.

⏱ 45-75 Mins Troubleshoot →

CODE E7 Altherma 3 H HT High

Outdoor DC Fan Motor Lock

Error E7 indicates that the outdoor unit inverter main PCB has detected a DC fan motor rotation failure, lock condition, or lack of Hall effect feedback signal while attempting to drive the fan.

⏱ 30-60 Mins Troubleshoot →

CODE E7-01 Altherma 3 H HT Critical

Outdoor Fan Motor Locked Rotor

Error E7-01 indicates an outdoor DC fan motor overload or locked rotor condition. The inverter PCB detects zero Hall IC feedback pulses or excessive motor winding current during startup or operation, frequently triggered in sub-zero ambient temperatures by ice entrapment around the fan cowl or internal motor bearing seizure.

⏱ 45-60 Mins Troubleshoot →

CODE L5 Altherma 3 Critical

Inverter Compressor Instantaneous Overcurrent

Error L5 triggers when the outdoor unit inverter printed circuit board (PCB) detects instantaneous overcurrent passing through the DC compressor output circuit, tripping the IPM (Intelligent Power Module) to prevent hardware destruction.

⏱ 45-60 Mins Troubleshoot →

CODE 7H-01 Altherma 3 Monobloc Critical

Water Flow Rate Error Fix

Error 7H-01 triggers when the primary vortex flow sensor detects a water flow rate below the minimum operational threshold (typically < 10-12 L/min depending on unit capacity) during pump operation, or when electrical signal feedback from the vortex sensor fails to register on the main control board, shutting down the compressor to prevent heat exchanger freezing or thermal runaway.

⏱ 30-45 Mins Troubleshoot →

CODE U0 Altherma 3 R MT Critical

Low Refrigerant Pressure Switch Trip

Error U0 indicates the low-pressure switch (S1PL) has tripped or the system detected an abnormal drop in suction pressure, typically below 0.15 MPa (R-32/R-410A circuit threshold), triggering compressor safety lockout.

⏱ 60-120 Mins Troubleshoot →

CODE L1 Altherma 3 H HT Critical

Inverter PCB Communication Fault

Internal serial communication loss between the outdoor main control PCB (A1P) and the compressor inverter driver PCB (A2P). The safety watchdog triggers an emergency lockout to protect the IPM and compressor.

⏱ 45-60 Mins Troubleshoot →

CODE U4 Sensira (FTXF / RXF Series) High

Indoor-Outdoor Transmission Failure

Error code U4 indicates a loss of serial data transmission between the indoor unit control PCB and the outdoor inverter main PCB across interconnecting terminal 3, causing an emergency shutdown.

⏱ 20-30 Mins Troubleshoot →