40 on a Hitachi heat pump: Incorrect unit controller setting
Short answer
On a Hitachi heat pump, 40 means: Incorrect unit controller setting. The heat pump stops until the fault clears or is reset. An engineer is needed to fix the cause. The wording differs by model range — each is shown below.
Reviewed 23 September 2026 · 2 sources
What it means
On the Yutaki H / H Combi (R32 hydrosplit)
The manual says: Incorrect unit controller setting.
Part involved: unit controller setting.
Likely causes:
- Current unit controller configuration does not allow proper operation.
On the Yutaki M (RASM monobloc)
The manual says: Incorrect unit controller setting.
Part involved: unit controller setting.
Likely causes:
- Current unit controller configuration does not allow proper operation.
On the Yutaki M (RHUE, 1st generation)
The manual says: Incorrect PCB operation.
On the Yutaki S (split air-to-water)
The manual says: Incorrect unit controller setting.
Part involved: unit controller setting.
Likely causes:
- Current unit controller configuration does not allow proper operation.
On the Yutaki S80 (high-temperature cascade split)
The manual says: Incorrect unit controller setting.
Part involved: unit controller setting.
Likely causes:
- Current unit controller configuration does not allow proper operation.
Is it safe?
On the Yutaki H / H Combi (R32 hydrosplit)
| 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.
On the Yutaki M (RASM monobloc)
| 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.
On the Yutaki M (RHUE, 1st generation)
| 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: Power OFF/ON to remove alarms in Yutaki M and system controller (TCGB0090 p.141 for F16/F17).
On the Yutaki S (split air-to-water)
| 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.
On the Yutaki S80 (high-temperature cascade split)
| 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.
- Check the room thermostat/controller display is powered and settings/timer are as expected.
What the engineer will check
On the Yutaki H / H Combi (R32 hydrosplit)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 40.
- 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.
On the Yutaki M (RASM monobloc)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 40.
- 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.
On the Yutaki M (RHUE, 1st generation)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 40.
- 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.
On the Yutaki S (split air-to-water)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 40.
- 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.
On the Yutaki S80 (high-temperature cascade split)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 40.
- 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.702 (viewer p.728) · Reviewed 23 September 2026
- YUTAKI M Series RHUE-3AVHN1 / RHUE-(3-6)A(V)HN-HM Technical Catalogue ↗ · TCGB0090 rev.0 - 12/2013 · page p.139 (PDF p.147) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026