151 on a Hitachi Yutaki S80: Excessively low or high voltage for the inverter (S80)
Short answer
On a Hitachi heat pump, 151 means: Excessively low or high voltage for the inverter (S80). 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: Excessively low or high voltage for the inverter (S80).
Part involved: S80 inverter voltage.
Likely causes:
- Described in inverter abnormal stop control.
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.
No need to switch off — call an engineer if it comes back.
Resetting itself: no.
Manual reset: Stop the unit (via unit controller / power off-on) after the cause is fixed.
What you can check
- Read and note the alarm code and any retry code (e.g. P70) shown on the unit controller.
- Check the heat pump supply breaker/isolator at the consumer unit is ON.
- Restart once via the unit controller (or switch off/on at the isolator) - the manual states the unit must be stopped to release most alarms; if the code returns, call an engineer.
What the engineer will check
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 151.
- Isolate power and wait for capacitor discharge before opening the electrical box.
- Check inverter PCB, IPM/DIP-IPM, current sensor wiring and connectors.
- Check compressor and fan motor windings; check heat exchanger for clogging.
Who to ask for: Heat pump service engineer (electrical/inverter diagnostics).
Certification: Competent electrical worker (BS 7671); isolate and wait 10 min for capacitor discharge.
What you might notice
Sources
- Service Manual - YUTAKI R32 / R410A series (Split, Monobloc and Hydrosplit systems) ↗ · SMGB0146 rev.0 - 12/2022 · page table printed p.657 (viewer p.683); troubleshooting flowchart printed p.744-745 (viewer p.770-771) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026