Heat pumps · Error codes · Joule
AP4Joule · Modul-AIR exhaust air heat pump
AP4 on a Joule Modul-AIR exhaust air heat pump: Pause mode - the compressor must not be started yet
Short answer
On a Joule heat pump, AP4 means: Pause mode - the compressor must not be started yet. The heat pump keeps running with some functions stopped.
Reviewed 23 September 2026 · 1 source
What it means
The manual says: Pause mode - the compressor must not be started yet.
Is it safe?
| Does the heat pump stop? | Partly |
|---|---|
| Severity | Information only |
| Engineer needed? | No |
The heat pump keeps running with some functions stopped.
What you can check
- Read and note the code shown on the controller display, then contact your installer or service engineer.
What the engineer will check
- Manual 'possible solution': (informational).
- Check running-hour counters and reset after scheduled maintenance per controller menu.
Who to ask for: heat pump service engineer.
Certification: None specific.
What you might notice
Sources
- Joule Modul-AIR All-E, Modul-AIR All-E with Green Comfort Module & Modul-AIR Aqua - Installation & Maintenance Manual ENG-0026-07 (UK/IE) ↗ · ENG-0026-07 · page 104 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026