S.133 on a Glow-worm GeniaAir: DHW generation: Pump prerun The start conditions for the compressor in domestic hot water mode are checked. Start the other actuators for domestic hot water mode
Short answer
On a Glow-worm heat pump, S.133 means: DHW generation: Pump prerun The start conditions for the compressor in domestic hot water mode are checked. Start the other actuators for domestic hot water mode. The heat pump keeps running.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: DHW generation: Pump prerun The start conditions for the compressor in domestic hot water mode are checked. Start the other actuators for domestic hot water mode.
Part involved: Heat pump control (status/Live Monitor).
When it shows: DHW generation: Pump prerun The start conditions for the compressor in domestic hot water mode are checked. Start the other actuators for domestic hot water mode.
Likely causes:
- Operating status reported by the heat pump control (not a fault in itself).
Is it safe?
| Does the heat pump stop? | No |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running.
Resetting itself: yes - status changes automatically with operating state.
Manual reset: not applicable.
What you can check
- Operating status only - no action needed. If heating or hot water is not being delivered for a long period, note the status code and tell your installer.
What the engineer will check
- None required unless heating/hot water is not delivered; then review status history, settings and application limits.
Who to ask for: Vaillant-trained heat pump installer/engineer (MCS-certified installer).
Certification: MCS installer certification; Vaillant product training recommended.
Sources
- GeniaAir Appliance Interface installation and maintenance instructions ↗ · 8000043014_01 · page HPIM 7 8000043014_01 p.27 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026