BUS-INITIALISING on a Dimplex A-Class air source heat pump: 'Bus Initialising' (from software 1.17 'Network Refreshing'): the indoor wiring centre cannot find the outdoor unit on the communication (Modbus) network
Short answer
On a Dimplex heat pump, BUS-INITIALISING means: 'Bus Initialising' (from software 1.17 'Network Refreshing'): the indoor wiring centre cannot find the outdoor unit on the communication (Modbus) network. 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: 'Bus Initialising' (from software 1.17 'Network Refreshing'): the indoor wiring centre cannot find the outdoor unit on the communication (Modbus) network.
Part involved: Modbus network: SEC board, master board, water module, user interface.
Likely causes:
- Corrupted SD card in wiring centre (water module).
- Power loss to outdoor unit.
- Loose connection or break in Modbus cable.
- Fault in SEC board, master board, water module or user interface.
Is it safe?
| Does the heat pump stop? | Yes |
|---|---|
| Engineer needed? | Yes |
The heat pump stops until the fault clears or is reset.
What you can check
- Check the outdoor unit isolator switch is ON.
- Check the consumer unit breakers for the heat pump are ON (reset once only).
What the engineer will check
- Power off, remove/reseat SD card and power up.
- Test Modbus cabling.
- Diagnose the four network components.
Who to ask for: heat pump service engineer.
Certification: Electrical competence (Part P / qualified electrician) for work inside control panels.
What you might notice
Sources
- GDHV Help Centre article: a class heat pump displaying bus initialising on the user interface what does this mean ↗ · GDHV article modified 2024-04-03 · page n/a (web article) · Reviewed 23 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 23 September 2026