31 on a Hitachi heat pump: Incorrect capacity setting or combined capacity between indoor and outdoor units
Short answer
On a Hitachi heat pump, 31 means: Incorrect capacity setting or combined capacity between indoor and outdoor units. 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: Incorrect capacity setting or combined capacity between indoor and outdoor units.
Part involved: capacity setting.
Likely causes:
- Incorrect capacity code setting (DSW3 on outdoor PCB); excessive or insufficient indoor unit total capacity code.
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 31.
- Check DIP switch capacity/model settings on indoor and outdoor PCBs.
- Check unit controller installer configuration.
Who to ask for: Commissioning engineer / MCS heat pump installer.
Certification: None specific.
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.654 (viewer p.680); troubleshooting flowchart printed p.699 (viewer p.725) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026