14 on a Hitachi heat pump: Indoor gas pipe refrigerant temperature thermistor anomaly (THMg)
Short answer
On a Hitachi heat pump, 14 means: Indoor gas pipe refrigerant temperature thermistor anomaly (THMg). 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: Indoor gas pipe refrigerant temperature thermistor anomaly (THMg).
Part involved: indoor gas pipe thermistor (THMg).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
On the Yutaki M (RASM monobloc)
The manual says: Indoor gas pipe refrigerant temperature thermistor anomaly (THMg).
Part involved: indoor gas pipe thermistor (THMg).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
On the Yutaki M (RHUE, 1st generation)
The manual says: Excessively high water temperature (compressor running).
On the Yutaki S (split air-to-water)
The manual says: Indoor gas pipe refrigerant temperature thermistor anomaly (THMg).
Part involved: indoor gas pipe thermistor (THMg).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
On the Yutaki S80 (high-temperature cascade split)
The manual says: Indoor gas pipe refrigerant temperature thermistor anomaly (THMg).
Part involved: indoor gas pipe thermistor (THMg).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
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
On the Yutaki H / H Combi (R32 hydrosplit)
- 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.
On the Yutaki M (RASM monobloc)
- 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.
On the Yutaki M (RHUE, 1st generation)
- 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 system pressure gauge on the indoor unit (Yutaki S / S Combi have a factory manometer; Yutaki M uses a field-fitted gauge) - Hitachi gives about 1.5-2.0 bar as normal and it must stay above 1 bar and below 3 bar.
- Check the filling loop is closed.
On the Yutaki S (split air-to-water)
- 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.
On the Yutaki S80 (high-temperature cascade split)
- 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
On the Yutaki H / H Combi (R32 hydrosplit)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 14.
- 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).
On the Yutaki M (RASM monobloc)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 14.
- 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).
On the Yutaki M (RHUE, 1st generation)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 14.
- Check water pump operation and fuse, pump feedback.
- Check all circuit valves open, clean strainers/filters (Filter+ valve).
- Check water pressure > 1 bar, bleed air, check flow and pressure switch/sensor continuity.
- Check heater contactors, water thermistors and minimum system water volume.
Who to ask for: Heating engineer / MCS heat pump installer.
Certification: G3 unvented qualification where a DHW cylinder is involved.
On the Yutaki S (split air-to-water)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 14.
- 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).
On the Yutaki S80 (high-temperature cascade split)
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 14.
- 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
- Service Manual - YUTAKI R32 / R410A series (Split, Monobloc and Hydrosplit systems) ↗ · SMGB0146 rev.0 - 12/2022 · page table printed p.653 (viewer p.679); troubleshooting flowchart printed p.681 (viewer p.707) · 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