Heat pumps · Error codes · Hitachi
59Hitachi · Yutaki S (split air-to-water)
59 on a Hitachi Yutaki S: Inverter fin temperature thermistor abnormality
Short answer
On a Hitachi heat pump, 59 means: Inverter fin temperature thermistor abnormality. 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: Inverter fin temperature thermistor abnormality.
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
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: unknown.
Manual reset: unknown.
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 59.
- Check thermistor/sensor connector seating and wiring on the PCB.
- Measure thermistor resistance against the characteristic table; replace sensor if out of range.
- Replace PCB if sensor and wiring are good.
Who to ask for: Heat pump service engineer.
Certification: None specific (electrical competence for PCB work).
What you might notice
Sources
- YUTAKI S Series Technical Catalogue (RWM-(H)FSN3E indoor units; RAS-H(V)RNME-AF / RAS-HVRN2 outdoor units) ↗ · TCGB0070 rev.3 - 04/2012 · page p.163 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026