F.752 on a Glow-worm GeniaAir: The frequency inverter reports an internal fault or an unknown compressor fault
Short answer
On a Glow-worm heat pump, F.752 means: The frequency inverter reports an internal fault or an unknown compressor fault. 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: The frequency inverter reports an internal fault or an unknown compressor fault.
Part involved: The frequency inverter reports an internal fault or an unknown compressor fault.
Likely causes:
- Internal electronics fault on the inverter PCB. Mains voltage outside of 70 V–282 V.
- Glow-worm trade page: Frequency convertor (invertor board) fault Incoming main voltage is not within permissible tolerances, electrical phases incorrect, reverse polarity, poor earthing, unstable power supply, fault in the wiring harness or connector to the invertor PCB, fault in the wiring harness or connector to the compressor, fault ….
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — 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
- 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. Glow-worm's MiPro Sense operating instructions say always contact your competent person in the event of a fault message; until they arrive you may select a limp-home (back-up heater) setting on the control, which is expensive to run.
What the engineer will check
- Check the integrity of the power supply cables and compressor connection cables. The plugs must audibly click into place. 2. Check cable. 3. Check the mains voltage. The mains voltage must be between 195 V and 253 V. 4. Check the phases. 5. 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.
What you might notice
Sources
- GeniaAir Appliance Interface installation and maintenance instructions ↗ · 8000043014_01 · page HPIM 7 8000043014_01 p.33 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026