8 on a Hitachi heat pump: Excessively high discharge gas temperature at the top of the compressor
Short answer
On a Hitachi heat pump, 8 means: Excessively high discharge gas temperature at the top of the compressor. 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: Excessively high discharge gas temperature at the top of the compressor.
Part involved: compressor discharge temperature.
Likely causes:
- Insufficient refrigerant charge, refrigerant leakage, expansion valve closed or clogged.
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.
- Check the outdoor unit is not blocked by snow, ice, leaves or debris and airflow around it is clear.
What the engineer will check
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 8.
- Check refrigerant charge and for leaks (F-gas qualified).
- Check expansion valve operation and strainers for clogging.
- Check heat exchanger/fan for blockage, pressure and temperature sensors.
- Check water flow (low flow causes high-pressure trips in heating).
Who to ask for: F-gas certified refrigeration / heat pump engineer (Hitachi Yutaki trained).
Certification: F-gas certificate (Category I); A2L (R32) flammable refrigerant training for R32 units.
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.652 (viewer p.678); troubleshooting flowchart printed p.675-676 (viewer p.701-702) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026