FD on a Mitsubishi Electric Ecodan Co2 Quhz: Detection of abnormal AC voltage: input voltage to outdoor unit 70 V or less
Short answer
On a Mitsubishi Electric heat pump, FD means: Detection of abnormal AC voltage: input voltage to outdoor unit 70 V or less. 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: Detection of abnormal AC voltage: input voltage to outdoor unit 70 V or less.
Part involved: Power supply / transmission line / earth leakage breaker.
When it shows: Input voltage to outdoor unit 70 V or less.
Likely causes:
- 1 Low power supply voltage (inappropriate supply, defective transmission line or connection); 2 Erroneous operation of earth leakage circuit breaker (switched back on before outdoor LEDs went out); 3 Defective outdoor inverter PCB.
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: Not stated as auto-recovering.
Manual reset: Outdoor error cancelled by switching the cylinder unit earth leakage circuit breaker OFF, waiting until the outdoor board LEDs go out (about 1 minute), then ON again (service manual GHH15010).
What you can check
- Note the code, unit and ref. address shown on the main remote controller and contact your installer (Mitsubishi user manuals: 'Make a note of the error code number and contact installer'). Check the heat pump breaker/isolator at the consumer unit is on and read the primary system pressure gauge (if fitted) so you can report it. A single reset from the main remote controller (RESET, then Yes) may be tried; if the code returns, do not keep resetting. Do not open the outdoor unit, cylinder/hydrobox or any casing. Check that the heat pump's dedicated breaker/isolator (and, where fitted, the separate indoor-unit supply) is switched on; if it trips again, leave it off.
What the engineer will check
- 1 Check supply voltage, replace/correct power transmission line; 2 Perform a reset (wait ~1 min for outdoor LEDs to go out before switching breaker back on); 3 Replace outdoor inverter PCB.
Who to ask for: Mitsubishi Ecodan-trained heat pump engineer (electrical / inverter diagnostics).
Certification: Competent electrician (BS 7671 / Part P); heat pump inverter experience.
What you might notice
Sources
- Ecodan QUHZ-W40VA Service Manual (GHH15010) ↗ · GHH15010 · page 16 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026