55 on a Hitachi heat pump: Abnormality of inverter module (inverter non-operation)
Short answer
On a Hitachi heat pump, 55 means: Abnormality of inverter module (inverter non-operation). 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: Abnormality of inverter module (inverter non-operation).
Part involved: inverter module.
Likely causes:
- Failure of DIP-IPM, IPM or 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.
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 55.
- 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.655 (viewer p.681); troubleshooting flowchart printed p.718 (viewer p.744) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026