19 on a Hitachi heat pump: Water plate heat exchanger pipe thermistor anomaly (THMwohp)
Short answer
On a Hitachi heat pump, 19 means: Water plate heat exchanger pipe thermistor anomaly (THMwohp). 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 · 1 source
What it means
On the Yutaki H / H Combi (R32 hydrosplit)
The manual says: Water plate heat exchanger pipe thermistor anomaly (THMwohp).
Part involved: water plate HEX pipe thermistor (THMwohp).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
On the Yutaki S (split air-to-water)
The manual says: Water plate heat exchanger pipe thermistor anomaly (THMwohp).
Part involved: water plate HEX pipe thermistor (THMwohp).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
On the Yutaki S80 (high-temperature cascade split)
The manual says: Compressor suction temperature thermistor anomaly (THMs) - S80 R134a stage.
Part involved: R134a compressor suction thermistor (THMs).
Likely causes:
- Loose, disconnected, broken or short-circuited connector.
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.
What the engineer will check
- Follow SMGB0146 section 6.7 troubleshooting flowchart for alarm 19.
- 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 · pages table printed p.653 (viewer p.679); troubleshooting flowchart printed p.687 (viewer p.713), table printed p.653 (viewer p.679); troubleshooting flowchart printed p.688 (viewer p.714) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026