Heat pumps · Error codes · Ariston
921Ariston · NIMBUS M HYBRID (UNIVERSAL) NET R32 hybrid kit
921 on an Ariston NIMBUS M HYBRID NET R32 hybrid kit: Error electricity/gas cost ratio
Short answer
On an Ariston heat pump, 921 means: Error electricity/gas cost ratio. The manual does not say whether the heat pump stops. An engineer is needed to fix the cause.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Error electricity/gas cost ratio.
Part involved: hybrid cost-ratio settings.
Likely causes:
- Configuration of parameters 1.13.0 and 1.13.1.
Is it safe?
| Does the heat pump stop? | Not stated |
|---|---|
| Engineer needed? | Yes |
The manual does not say whether the heat pump stops.
What you can check
- Note the error code shown on the Sensys HD interface and contact the installer / Ariston service.
What the engineer will check
- Verify the configuration of parameters 1.13.0 and 1.13.1.
What you might notice
Sources
- NIMBUS HYBRID MODULE UNIVERSAL NET R32 (code 3301801) - Technical instructions for installation and maintenance (UK), doc 420000657300 EN ↗ · 420011313000 - 04/2023 · page 84 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026