F.757 on a Glow-worm GeniaAir: During heat pump mode, the compressor running time fell below the minimum level too frequently
Short answer
On a Glow-worm heat pump, F.757 means: During heat pump mode, the compressor running time fell below the minimum level too frequently. 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: During heat pump mode, the compressor running time fell below the minimum level too frequently.
Part involved: During heat pump mode, the compressor running time fell below the minimum level.
Likely causes:
- The compressor stopped several times before the minimum running time was reached. The product was therefore blocked. In systems without buffers and with a low volume of heating water, the temperature can rise or fall extremely quickly when the compressor starts. Depending on the start conditions, there is a risk that the product will stop.
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 that radiator/underfloor valves are not all closed (the fault is linked to too little circulating water). 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 circulation hot water volume. 2. If required, increase the circulation hot water volume. 3. Check the bypass valve.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS installer certification; Vaillant product training recommended.
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