02-g1 on a Hitachi Yutaki M: Excessively low temperature of heat exchanger refrigerant inlet
Short answer
On a Hitachi heat pump, 02-g1 means: Excessively low temperature of heat exchanger refrigerant inlet. 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 low temperature of heat exchanger refrigerant inlet.
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: Power OFF/ON to remove alarms in Yutaki M and system controller (TCGB0090 p.141 for F16/F17).
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 02-g1.
- 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
- 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