78 on a Hitachi heat pump: RF communication failure (intelligent thermostat accessory)
Short answer
On a Hitachi heat pump, 78 means: RF communication failure (intelligent thermostat accessory). 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: RF communication failure (intelligent thermostat accessory).
Part involved: RF bridge.
Likely causes:
- No communication for 1 hour with one or two RF receivers bound to the RF-Bridge.
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 room thermostat/controller display is powered and settings/timer are as expected.
What the engineer will check
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 78.
- Check H-Link / transmission wiring polarity, continuity and terminal tightness.
- Check PCB fuses and DIP-switch/address settings.
- Check power to the other unit (outdoor/indoor/controller).
Who to ask for: Heat pump installer / service engineer (controls wiring).
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.656 (viewer p.682); troubleshooting flowchart printed p.731 (viewer p.757) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026