The network voltage is low or unstable
Plates are dimly lit, flickering, or working one day and not the next. Intermittent faults that move around the house are the signature of a network running short of power, and they are the most misdiagnosed fault in C-Bus.
The C-Bus network is not holding a healthy voltage. Either the supply is failing, or more units are drawing from it than it was sized for, or a wiring fault is loading it down.
Why this one gets misdiagnosed so often
Because it does not present as one fault. It presents as a series of unrelated small faults: a plate that is dead this morning and fine this afternoon, a switch at the far end of the house that has become unreliable, scenes that fire completely most times and partly other times. Each individual symptom looks like a separate failing unit, and houses in this state have often had several perfectly good switches replaced before anyone measured the network.
The tell is geography. Voltage problems hit the units furthest from the supply first, so if your unreliable plates are all at one end of the house, or all on one branch, that is the pattern rather than coincidence.
This one is mains work. Stop here and book a licensed electrician. Switchboards, DIN-rail power supplies, dimmer and relay modules, and anything behind a faceplate are all live electrical work. There is no safe DIY version of this check.
Ask for an electrician with C-Bus accreditation if you can get one. A general electrician can safely isolate, test and replace hardware, but most cannot program the system afterwards, which is the half that makes your lights behave again.
How a system that worked for years ends up here
- The system grew
- Every unit draws a share of the network's power budget. Extensions, a new touchscreen, extra sensors: each is small, and collectively they can exceed what the original supply was sized for.
- The supply is weakening
- Power supplies degrade before they fail outright. A unit delivering less than it used to produces exactly this creeping unreliability.
- A wiring fault is loading it
- A partial short, water in an outdoor junction, or a damaged cable pulls voltage down without stopping the network completely.
- A unit is failing wet
- A single water-damaged unit can draw far more than it should and drag the whole network down with it. Fixing that one unit fixes the network.
Why it needs measuring, not guessing
All four causes above produce the same symptoms, and you cannot tell them apart from the wall. Someone has to measure the bus voltage, ideally at more than one point, and add up what is actually connected against what the supply provides. That is an hour of competent work that saves you from the alternative, which is replacing units one at a time for a year while the real problem stays put.
If you have already replaced a switch or two without the problem going away, that history is itself evidence. Mention it: it moves the diagnosis towards the network and away from the units, and it saves the next person repeating the same experiment.
How it is corrected
Depending on what the measurement finds: an additional or larger power supply, splitting the network into segments with their own supplies, repairing the wiring fault, or removing the one unit that is misbehaving. None of these touch your switches, your programming or your cabling in any structural way. This is tuning a system back into its designed operating range, not rebuilding it.
Faults that move around and never quite reproduce?
That pattern is worth describing in detail: which plates, which end of the house, and whether it correlates with weather. We measure the network before recommending any parts.