C-Bus Lights
Stuck On
Relay Fault. Act Now.
If your C-Bus lights won't turn off regardless of what you do — switches, app, or scene commands — you most likely have a welded relay contact. This is a hardware fault in the output unit, not a programming issue. It creates an ongoing energy waste, heat build-up inside the panel, and in some cases a compliance risk. Don't leave it running.
Are You Seeing
These Signs?
These are the specific symptoms that point to this fault. If you're seeing two or more, call now — don't wait for total failure.
- One or more lighting circuits stay on regardless of switch commands
- The C-Bus App shows the group OFF but the load remains energised
- Cycling power to the relay output unit briefly turns the circuit off, but it comes straight back on
- The output unit enclosure feels unusually warm to touch
- Specific zones have been stuck ON for days or weeks
- Related circuits function normally — only specific channels are stuck
- You can hear the relay clicking but the load doesn't respond correctly
What's
Actually Wrong
These are the physical causes behind this fault — in order of likelihood. We trace the root cause before any parts are replaced.
Welded Relay Contact — Permanent ON
Relay contacts are rated for a specific number of switching cycles — typically 100,000–200,000 operations at rated load. After years of daily switching, the contacts can weld together in the closed (ON) position under the arc of switched current. The relay coil still operates but the contacts don't open. Result: permanent circuit energisation regardless of commands.
Relay Contact High-Resistance Arc — Intermittent
Before full welding, relay contacts develop a high-resistance film from arcing. The contact technically opens and closes, but with reduced voltage delivery. This causes flickering, delayed OFF response, and intermittent stuck-ON behaviour before complete weld failure.
Relay Output Unit Firmware / Logic Fault
Occasionally, a stuck-ON condition is caused by a corrupted ON command logged in the output unit's non-volatile memory. The unit is executing a stored command rather than following real-time network state. Resolvable via C-Bus Toolkit without hardware replacement.
Overloaded Output Channel
A relay channel that has been operating at or beyond its rated load (amps) for years can fail in the ON state due to thermal damage to the contact assembly. Particularly common in systems that had LED retrofits without re-checking per-channel load ratings.
What to Do
Right Now
Before we arrive — these steps protect your system from further damage.
If specific lights or circuits are stuck on and you can identify the relevant circuit breaker, isolating it prevents energy waste and removes the heat risk from the relay output unit while we arrange attendance.
Cycling the relay rapidly via switches or the app while it's fault-stuck can cause additional arcing and accelerate contact damage. Leave it in state.
Record the zone name or switch label, and if accessible, the output unit address or physical location in the panel. This helps us bring the right replacement unit.
Describe the fault. We carry common relay output units and will either repair the existing unit or replace it on-site.
From Call to
Fixed — Fast
No runaround. No subcontractors. No second appointments.
Call or SMS
Describe your fault. We triage immediately and confirm attendance for the same day or next available slot. You speak directly with George — no call centres.
⏱ 5 minutesOn-Site Attendance
We attend with C-Bus Toolkit, test equipment, and common spare parts. The person on the phone is the person who shows up.
⏱ Same day where possibleFault Diagnosis
We connect to the network, read the system file, and trace the fault methodically. You get a clear explanation before any work proceeds.
⏱ Usually 30–60 minRepair & Restore
Most faults are fixed in a single visit. We carry common C-Bus spares and source directly from Schneider where needed. System documented before we leave.
⏱ Most faults: 1 visitStraightforward
Pricing
Fixed labour rates, no hidden fees. All work quoted before proceeding. Parts additional at cost.
- Monday–Friday, 7am–5pm
- Fault diagnosis & repair
- C-Bus Toolkit connection included
- Written fault report
- Parts additional at cost
- Priority same-day scheduling
- Fault diagnosis & repair
- C-Bus Toolkit connection included
- Written fault report
- Parts additional at cost
- Strata & commercial welcome
- Evenings, weekends & public holidays
- Fault diagnosis & repair
- C-Bus Toolkit connection included
- Written fault report
- Parts additional at cost
All rates are for labour only. Replacement parts and consumables are additional and quoted before supply. No GST applicable — ABN 61 136 364 150.
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Emergency Guides
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Quick
Answers
Can a welded relay contact be fixed without replacing the whole output unit?
Not reliably. A welded contact is a permanent mechanical failure of the relay. The relay assembly inside the output unit needs replacement — which in practice means replacing the output unit. We carry common models and can typically replace on-site.
Is a stuck-ON C-Bus relay a fire risk?
A welded relay contact energises the load continuously, which creates heat inside the enclosure and increases load on the circuit. While it rarely leads to a fire directly, it creates conditions that can degrade surrounding components and wiring over time. It should be treated as urgent.
My C-Bus app shows the group is OFF but the lights are still on — is this definitely a relay fault?
Yes, in almost all cases. The C-Bus network is commanding the circuit OFF and the output unit is acknowledging the command (which is why the app shows OFF), but the physical relay contact is stuck closed. The network is doing its job — the hardware isn't.
How long can I run with a stuck-ON relay before it becomes a serious problem?
The primary ongoing risks are energy waste (the circuit runs 24/7) and heat build-up in the output unit. The longer it runs, the more heat stress accumulates in the surrounding enclosure — which can affect adjacent units. It should be repaired as soon as practical.
I turned off the circuit breaker and the load went off — but it came back on when I restored power. Is this normal?
No. If the load returns immediately on power restoration without a command being sent, the relay is definitely stuck closed. The brief power interruption doesn't fix the welded contact — it just confirms the fault.
Send Us a
Message
Fill out the form and we'll get back to you fast — usually within the hour during business hours. For urgent faults, call 0422 469 739 directly.
C-Bus Down?
Don't Wait.
Every hour a failed C-Bus system runs in a fault state, more damage cascades through the network. Call now and we'll get it sorted — same day where possible.