F.818 on a Glow-worm GeniaAir: The mains voltage at the frequency inverter is not available or outside of the tolerances
Short answer
On a Glow-worm heat pump, F.818 means: The mains voltage at the frequency inverter is not available or outside of the tolerances. 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 mains voltage at the frequency inverter is not available or outside of the tolerances.
Part involved: The mains voltage at the frequency inverter is not available or outside of the t.
Likely causes:
- Incorrect mains voltage for operating the frequency converter. Shutdown via the energy supply company; The mains voltage must be between 195 V and 253 V. Code/meaning Possible cause Measure.
- Glow-worm trade page: Frequency convertor (invertor PCB) fault – Mains voltage fault Incoming main voltage is not within permissible tolerances, electrical phases incorrect (400V versions only), reverse polarity, poor earthing, unstable power supply.
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
- Measure and, if required, correct the mains voltage.
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