C-Bus fault diagnoser
Start with what has stopped working. A few questions later you will know which part of the system is the likely culprit, whether it is even a C-Bus problem, and what to ask for when you call someone.
This tool is built for the situation almost every C-Bus owner ends up in: the system was installed years ago, the installer has moved on, and no one will give you a straight answer about what is wrong. It will not fix your lights. What it will do is turn "half the house does not work" into "the relay module feeding the west circuits has failed", which is the difference between a quote you can trust and a quote you cannot check.
Nothing on this page asks you to take anything apart. Every check here is done by looking, or by pressing buttons that are already on the outside of a wall plate. Opening the hinged door of your switchboard to see the breakers is normal and fine. Removing the panel behind them is not, and neither is unscrewing a wall plate or lifting the cover off an enclosure.
In Australia it is illegal to work on fixed wiring without an electrical licence, and the reason is not paperwork: the terminals behind a C-Bus wall plate can be sitting at mains voltage. Anything past the faceplate is a job for a licensed electrician, ideally one with C-Bus accreditation.
What has stopped working?
Pick the closest match. If two fit, start with the smaller one: it is faster to rule out.
- One switch does nothingA single wall plate or a single key on it has gone dead. Everything else in the house behaves normally.
- One room or one group of lights is deadA whole area has stopped responding, but switches elsewhere still work.
- Nothing responds anywhereThe whole system is unresponsive. Lights may be stuck on, stuck off, or dead across the house.
- Lights work, but the scenes and timers are wrongButtons do something, just not the right thing. Scenes fire half-way, or at the wrong time of day.
- Lights turn on or off by themselvesLights change state with nobody touching anything, at random or at oddly consistent times.
- It stopped after a blackout or stormEverything was fine until the power went out. It came back, and the lighting system did not.
- The PC or touchscreen that ran it has diedThe computer or wall touchscreen that controlled the system is gone, and nobody has the files.
If you have just inherited the system
If you bought the house and the C-Bus came with it, the fault is only half your problem. The other half is that you do not yet know what you own. Start with the guide to an inherited C-Bus house, which covers what the hardware is, why the wiring is worth more than the electronics, and what your realistic options are. Then come back here when you want to chase a specific fault.
Why this works without any tools
C-Bus wall switches are not switches in the ordinary sense. They are small networked computers that send a message to a separate unit, usually mounted on a DIN rail in an enclosure, which does the actual switching. Because of that split, the indicator LEDs on the wall plate tell you which half of the conversation is broken: whether the switch is alive and being heard, or whether nothing is listening. That single observation removes most of the guesswork, and it costs nothing but looking. There is more detail in what your switch LEDs are telling you.
Last reviewed: 14 August 2026. General guidance only. A diagnosis over the internet is a starting point, not a substitute for someone competent looking at your actual system.
Would rather just have someone sort it out?
Send us the symptoms, a photo of the wall plate and a photo of the enclosure. We work on C-Bus specifically, including systems with no files and no history, and we will tell you what we think it is before we book anything.