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Heat pumps · Error codes · Vaillant
F.752Vaillant

F.752 on a Vaillant heat pump: Fault: Frequency converter

Short answer

On a Vaillant heat pump, F.752 means: Fault: Frequency converter. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause.

Reviewed 23 September 2026 · 2 sources

What it means

On the aroTHERM plus (VWL ../6 A)

The manual says: Fault: Frequency converter.

Part involved: Frequency converter.

When it shows: Internal electronics fault on inverter PCB or mains voltage outside 70-282 V; follows S.575 occurring three times.

Likely causes:

  • Internal electronics fault on the inverter PCB; Mains voltage outside of 70 V–282 V.

On the aroTHERM

The manual says: Fault: Frequency converter.

Part involved: Frequency converter.

Likely causes:

  • 'Max. duration power supply cut-off' poorly set; inverter box damaged; inverter box cooler blocked; faulty power supply.

Is it safe?

Does the heat pump stop?Yes
SeverityFault — needs a manual reset once the cause is fixed
Engineer needed?Yes

The heat pump stops until the fault clears or is reset.

Resetting itself: no - the fault remains displayed until the cause is eliminated.

Manual reset: yes - after the cause is eliminated, press the reset button (indoor unit) or reset via the system control; if it recurs after several resets contact customer service.

What you can check

On the aroTHERM plus (VWL ../6 A)

  • Note the full code and text shown on the display (and the date/time it appeared). Check the heat pump supply breaker/isolator (and back-up heater breaker, if separate) at the consumer unit is on; if a breaker has tripped more than once, leave it off and call an engineer - do not open any casing. The operating instructions allow the reset button on the indoor unit (or a reset via the system control) to be pressed once; if the code returns, do not keep resetting - contact your installer or Vaillant.

On the aroTHERM

  • Note the full code and text shown on the display (and the date/time it appeared). Check the heat pump supply breaker/isolator (and back-up heater breaker, if separate) at the consumer unit is on; if a breaker has tripped more than once, leave it off and call an engineer - do not open any casing. Do not keep resetting the unit; report the code to your installer (the operating instructions for this product were not checked for a homeowner reset procedure).

What the engineer will check

On the aroTHERM plus (VWL ../6 A)

  • Check the integrity of the power supply cables and compressor connection cables The plugs must audibly click into place; Check the cable; Check the mains voltage The mains voltage must be between 195 V and 253 V; Check the phases; Replace the frequency converter, if required.

Who to ask for: Heat pump engineer with electrical competence (qualified electrician for supply/phase faults).

Certification: Competent electrician (BS 7671 / Part P) for supply-side work.

On the aroTHERM

  • Diagnose per cause list in the aroTHERM installer fault table; inform Vaillant technical support (0330 100 3540) for refrigerant-circuit faults.

Who to ask for: Heat pump engineer with electrical competence (qualified electrician for supply/phase faults).

Certification: Competent electrician (BS 7671 / Part P) for supply-side work.

What you might notice

What owners and engineers report

17 owner and engineer reports mention this.

  • No heating on the aroTHERM plus (VWL ../6 A): 8 reports
  • No hot water on the aroTHERM plus (VWL ../6 A): 5 reports
  • Heat pump will not start on the aroTHERM plus (VWL ../6 A): 2 reports
  • No heating on the aroTHERM: 2 reports

Sources

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

Reviewed: 23 September 2026