Diagnosing Visual Alarm Device (VAD) Faults on a Fire Alarm System
Visual alarm devices get less attention than sounders in most fault call-outs, largely because a silent VAD is far less noticeable than a silent sounder circuit — nobody in the building is listening for a flash the way they listen for a bell. That makes VAD faults easy to under-investigate, and it makes one particular fault, unsynchronised flashing, worth taking as seriously as an outright failure, because it is treated as a safety issue in its own right rather than just an inconvenience.
The essential idea is this: a VAD fault diagnosis has to check three separate things — the circuit's electrical health, the device's actual light output, and whether multiple devices in the same space are flashing together — because a fault in any one of them can exist while the other two look completely normal.
Who this is for
This is for fire alarm engineers responding to a visual alarm device fault, a reported synchronisation problem, or verifying VAD performance as part of a proving test. Experience level: competent engineer, comfortable with sounder and VAD circuit wiring and with the difference between electrical continuity and confirmed physical output. No default access codes, engineer-level entry procedures or internal service routines are published here.
What counts as a VAD fault, and what the panel might not see
A visual alarm device is typically wired on a circuit shared with, or similar in design to, a sounder circuit, and where that circuit is electrically supervised the panel can detect an open circuit or short circuit the same way it monitors any other output. BS EN 54-23 sets requirements for VAD performance, including light output and coverage, but electrical circuit supervision and confirmation of actual flash output are not the same thing, and many designs supervise only the former.
What the panel generally cannot see is whether the device is actually flashing correctly. A xenon tube that has failed, an LED array with a failed driver, or a mechanical fault in the lens assembly can all leave a device silent — visually, in this case — while the circuit wiring it sits on reads perfectly healthy. This mirrors the same silent-failure risk found in relay and output circuits: a clean circuit reading is reassuring about the wiring, and says nothing about the device's actual physical behaviour.
Telling a circuit fault, a device fault and a synchronisation fault apart
A reported circuit fault, where the circuit is supervised, points toward the wiring first: an open circuit, a short circuit, or a device reporting an internal fault of its own, and this narrows down the same way any supervised circuit fault does — test continuity progressively along the circuit to bracket where the fault sits.
A single failed device on an otherwise healthy circuit is different and usually only found by physical observation: everything reads correctly electrically, but one VAD among several on the same circuit does not flash during a test while its neighbours do. This is why a proving test needs to include watching every VAD actually flash, not just confirming the panel shows the circuit as healthy.
A synchronisation fault is different again, and in a category of its own because of what it represents rather than what causes it. Multiple VADs within sight of each other in the same space are required to flash in a coordinated pattern rather than independently, addressed directly by BS EN 54-23 and BS 5839-1, because uncoordinated flashing can be confusing to occupants and carries a recognised photosensitivity risk for some individuals. Many designs do not independently supervise synchronisation as a distinct fault condition, which means this has to be checked by direct observation during testing rather than assumed from an absence of any panel-reported fault.
On arrival and initial observations
Read the panel display and event log for the exact wording, and establish whether there is a reported circuit fault, a specific complaint about a device not flashing or flashing out of sync, or whether this visit is a routine proving test. Identify how many VADs sit within sight of each other in the affected space, since synchronisation only matters where more than one is visible from a given viewpoint.
Ask what has changed. A recently added VAD to an existing circuit or synchronisation group, a device replaced without confirming it matched the synchronisation protocol of the others, or building alterations changing which devices are now visible from a given point are all things the site knows and the panel cannot tell you.
Evidence gathering and site observations
Record the exact fault wording or the specific complaint before disturbing anything, and where a synchronisation issue is reported, note the viewpoint from which it was observed and which devices were visible from there. Photograph the circuit's supervised readings where available.
Site observations matter because VADs are frequently added to a building incrementally — an extension, a refurbished area, an accessibility improvement — and a device added later, from a different production batch or even a different manufacturer if the circuit is not protocol-specific, is a common and easily overlooked cause of a synchronisation mismatch that a purely electrical check would never reveal.
What you can safely establish on site
Within the limits of your authorisation, test circuit continuity and, where the design allows, isolate individual devices to bracket a circuit fault the same way as any other supervised circuit. Operate a genuine test alarm and physically observe every VAD in the affected area flash, rather than relying on the panel's circuit status alone. Where more than one VAD is visible from a single viewpoint, observe them together during the test specifically to confirm they flash in a coordinated pattern, not just that each flashes individually.
Safety warning. VAD flash rates and intensities are specified for a reason connected to photosensitivity and occupant alerting, and any replacement device must match the synchronisation protocol, flash rate and light output class of the others in the same group — fitting a compatible-looking but non-matching device can silently reintroduce a synchronisation fault that looks, electrically, like a successful repair.
Investigation flowchart
Used as an investigation flowchart, the sequence runs:
- Read the panel display and event log, and establish whether this is a circuit fault, a device complaint, a synchronisation report, or a routine proving test.
- Identify how many VADs are visible together from any single viewpoint in the affected space.
- Test circuit continuity and bracket the fault location if a supervised circuit fault is reported.
- Operate a genuine test alarm and physically observe every VAD in the area flash.
- Where multiple VADs are visible together, observe them specifically for coordinated versus independent flashing.
- If a single device fails to flash on an otherwise healthy circuit, treat that device as the fault.
- If devices flash independently rather than together, treat synchronisation as the fault, even with no panel-reported condition.
- Confirm any replacement device matches the synchronisation protocol, flash rate and light output class of the group.
- Retest the full group together after any repair or replacement.
- Report the finding, including whether this was a synchronisation issue the panel never flagged, to the responsible person.
Repair, verification and testing after repair
Verification after a VAD repair means physically observing the repaired or replaced device flash correctly during a genuine test, and, where it sits within sight of other VADs, observing the whole group together to confirm synchronisation, not just the one device in isolation. A replacement device that flashes correctly alone but has not been confirmed against its synchronisation group can still leave an unresolved fault behind.
A short repair checklist for this class of work: circuit continuity confirmed healthy; every VAD in the affected area physically observed to flash on test; VADs visible together from any viewpoint confirmed to flash in a coordinated pattern; any replacement device confirmed to match protocol, flash rate and light output class; logbook and, where applicable, the fire strategy documentation updated.
Escalation and spares
Escalate to the manufacturer's technical support when a device's documented synchronisation behaviour does not match what testing shows, or when mixed-generation or mixed-manufacturer devices on the same circuit cannot be confirmed compatible from the documentation available. A good escalation includes the panel and device models, the circuit and synchronisation group involved, and what has already been eliminated.
Standard VAD units are usually straightforward to source, but matching a replacement to an existing synchronisation group's exact protocol and flash characteristics is the part most likely to need manufacturer confirmation, particularly on older installations where the original model has since been superseded. Estimated repair time is typically same-visit for a single device swap, extending where compatibility with an existing group needs to be confirmed before fitting.
Common engineer mistakes
Treating a healthy circuit reading as confirmation every VAD on it actually flashes, without physically observing each one during a test. Fixing a single failed device and not retesting it alongside the other VADs it should synchronise with. Fitting a replacement device that looks physically similar without confirming it matches the synchronisation protocol and flash rate of the group. Not checking for synchronisation faults at all where the panel has no specific supervision for it, on the assumption that no fault reported means nothing is wrong. And overlooking a device added during unrelated building work that has quietly introduced a mismatch into an existing group.
Telling the responsible person
There is a legal dimension worth being clear about. In England and Wales the Regulatory Reform (Fire Safety) Order 2005 places duties on the responsible person, including a maintenance duty in respect of the fire safety equipment provided in the premises. BS 5839-1 and BS EN 54-23 are, respectively, a code of practice and a product standard giving recommendations and requirements for visual alarm devices; neither is itself legislation.
What that means in practice is straightforward, and worth being direct about: an unsynchronised group of VADs is not simply a cosmetic issue, and the responsible person should understand it as a genuine alerting and, for some occupants, a photosensitivity concern, addressed specifically for that reason rather than treated as a minor snag.
Report example
A workable report example: "Complaint received that visual alarm devices in the open-plan office area appeared to flash out of step during a fire drill. No fault indicated at panel prior to investigation. Circuit continuity confirmed healthy throughout. Test alarm operated and all four VADs in the area observed: three flashing in coordinated pattern, one flashing independently at a different rate. Device found to be a replacement fitted during a recent office refurbishment, of a different model to the original synchronisation group, without confirming protocol compatibility. Replaced with a matching unit confirmed against manufacturer documentation for the same synchronisation protocol and flash rate; retested with all four devices together and confirmed coordinated. No fault had been shown at the panel at any point — recommend any future device additions or replacements be confirmed against the existing group's protocol before fitting."
Related faults
Related faults worth reading alongside this: visual alarm devices and BS EN 54-23 for the design and coverage principle behind these devices, sounder and beacon synchronisation explained for the general synchronisation concept this fault sits against, and fault-finding a fire alarm sounder circuit that won't sound for the equivalent audible-output fault this diagnostic approach mirrors.
When not to rely on this alone
When not to use this article: do not use it to design VAD coverage or synchronisation grouping for a specific building, to select a light output class for a space, or to decide a replacement device is compatible without confirming its protocol against the manufacturer's documentation. The first two come from BS 5839-1, BS EN 54-23 and the fire strategy applied by a competent designer, and the third is exactly the assumption this article argues against.
Relevant standards
Recommendations for VAD coverage and use sit within BS 5839-1, current edition, with performance and synchronisation requirements for the devices themselves set out in BS EN 54-23, current edition. These are standards, not law; the statutory duty in England and Wales rests with the responsible person under the Regulatory Reform (Fire Safety) Order 2005. Work to the current edition in every case and to the manufacturer's documentation for the installed visual alarm device.
Professional disclaimer
This is an educational resource for competent engineers. It does not replace the current British Standards, the manufacturer's documentation or professional judgement. Confirm any replacement device's synchronisation protocol, flash rate and light output class against the manufacturer's documentation, and verify actual physical flash output and group synchronisation, not panel circuit status alone.
Related documentation
Read this with visual alarm devices and BS EN 54-23 and sounders and visual alarm devices: audibility, coverage and the alerting principle. Recording VAD faults, synchronisation checks and their resolution is easier with the fault database and the digital logbook.
References
- BS 5839-1 (current edition), BSI
- BS EN 54-23 (current edition), BSI
- The Regulatory Reform (Fire Safety) Order 2005 — legislation.gov.uk
- Visual alarm device manufacturer installation and fault-finding documentation for the equipment on site