Heat pumps · Error codes · Joule
38Joule · Modul-AIR exhaust air heat pump
38 on a Joule Modul-AIR exhaust air heat pump: Lost communication between ComfortZone UFH wiring centre and the Green Comfort Module
Short answer
On a Joule heat pump, 38 means: Lost communication between ComfortZone UFH wiring centre and the Green Comfort Module. 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: Lost communication between ComfortZone UFH wiring centre and the Green Comfort Module.
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.
Manual reset: Installer override required.
What you can check
- Read and note the code shown on the controller display, then contact your installer or service engineer.
- Check the heat pump's breaker/isolator at the consumer unit is switched on (do not repeatedly reset if it trips).
What the engineer will check
- Manual 'possible solution': Check cable. Replace if necessary.
- Check communication cable between controller/PCB/driver board (type, polarity, termination).
- Check power supply to the remote module.
- Replace faulty PCB/controller if wiring is sound.
Who to ask for: heat pump controls / electrical.
Certification: Electrical competence.
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 105 · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026