Heat pumps · Error codes · IVT
GT9IVT · Greenline HT Plus
GT9 on an IVT Greenline HT Plus: High return to the heat pump T9 (GT9): compressor stopped because return water temperature is too high (limit approx. 58°C)
Short answer
On an IVT heat pump, GT9 means: High return to the heat pump T9 (GT9): compressor stopped because return water temperature is too high (limit approx. 58°C). 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: High return to the heat pump T9 (GT9): compressor stopped because return water temperature is too high (limit approx. 58°C).
Part involved: return sensor GT9.
Likely causes:
- Heating setting too high; radiator/floor valves closed; hot water temperature set too high (alarm in hot water mode); flow across heat pump greater than heating system flow (bypass fitted).
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
Resetting itself: Yes.
What you can check
- Lower the heating setting (Temp. incr./decr.) on the controller; make sure radiator/underfloor valves are open; then press Ackn. If it occurs in hot water mode, ask the installer to adjust the hot water temperature.
What the engineer will check
- Adjust heat carrier/main pump speeds where a bypass is fitted; check hot water setting.
Who to ask for: heat pump engineer.
What you might notice
Sources
- Greenline HT Plus C and E Guide to installation, commissioning and maintenance (Art. no 290410-29, v1.1) ↗ · 290410-29 v1.1 · page p.38 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026