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Troubleshooting

A BACnet scan finds no devices​

This is almost always a network or permission issue, not a device fault. Check, in order:

  1. Local Network permission (iOS). BacBus needs Local Network access to send the Who-Is broadcast. Check Settings → BacBus → Local Network is on. If you denied it on first launch, enable it here and scan again.
  2. Same subnet/VLAN. Who-Is is a UDP broadcast and does not cross routed subnets. Your phone must be on the same broadcast domain as the controllers. Joining "the building Wi-Fi" isn't enough if it routes to a different subnet than the controls network.
  3. Wi-Fi actually connected. Confirm you're on Wi-Fi (not cellular) and that the network reaches the controls VLAN.
  4. Devices use a non-standard port. BacBus uses the standard BACnet/IP port (UDP 47808). Devices on a different port won't answer the broadcast.

:::info Empty is a valid result On a network with no BACnet equipment — a typical office Wi-Fi — a scan correctly returns nothing. There's simply nothing on the wire to answer the Who-Is. :::

A device is found but its object list is empty or partial​

  • Tap ↻ Rescan to retry — a busy device can drop reads under load.
  • Very large devices with many objects take longer; let the scan finish (the header shows live progress).
  • Stay on a stable connection during the scan; moving between access points mid-scan can interrupt reads.

A BACnet write didn't take​

  • Priority. A higher-priority command masks yours. Open the object's priority array to see which level is in control, and either write at a higher priority or relinquish the masking level.
  • Read-back. After a write, BacBus re-reads the object. If the value snapped back, something else is commanding it (a schedule, another tool, or the control program) — check the priority array.
  • Clamping. Devices clamp out-of-range values. The read-back shows what was actually applied.

A point is stuck in override​

Open the object, expand Show priority array, and Relinquish the level holding the override — or Relinquish all to clear every commanded slot. Control returns to the next-lower priority or the relinquish-default. Relinquish and writing require Pro.

Modbus connection fails​

  • Verify Host/IP and Port (default 502) and that the device is reachable from your phone's network.
  • Check the Unit id. If you're not sure, use 🔢 Scan unit IDs to find the responding ids — and note that some gateways answer every id with the same data.
  • Behind a TCP→RTU gateway, the gateway's IP is the host; the RTU slave address is the unit id.

Modbus reads return wrong numbers​

  • Data type. Make sure the Type matches how the device stores the value (e.g. float32 vs two uint16 registers).
  • Word order. For 32-bit types, try the other Word order options (ABCD / CDAB / BADC / DCBA) until the value reads correctly — vendors differ.
  • Addressing offset. Some documentation uses 1-based addresses (e.g. 40001) while the protocol is 0-based. Adjust Start accordingly, or use 🔎 Discover points to find the real mapped addresses.

A Pro feature is locked​

Writing, relinquishing, and CSV export require a one-time BacBus Pro unlock. If you already purchased Pro but it shows as locked (for example on a new phone), open the Pro screen and tap Restore purchase.

Still stuck?​

Reach us through harnessautomation.com.