Summary

Video intercom (door entry) systems range from simple two-wire audio-only units in a single house to multi-panel, multi-monitor video systems serving blocks of flats, and increasingly to IP-based or Wi-Fi connected systems that stream to a resident's phone rather than (or as well as) a wall-mounted monitor. Each of these architectures fails differently, and a fault-finding approach that works on an old analogue two-wire system will send you down the wrong path on a PoE (Power over Ethernet) IP intercom.

The most common misconception tradespeople bring to a callout is assuming the fault is at the point where the symptom shows up — no picture on the monitor, so the camera must be broken. In practice, video intercom faults are disproportionately caused by power supply issues, loose or corroded connections at the external panel (which takes the weather), or — on communal systems — a fault introduced somewhere else in the daisy-chain wiring that affects every flat downstream of it, not just the one reporting the problem.

Communal (block of flats) systems add two further complications that a domestic-only installer needs to be aware of: the door release is frequently interfaced with the building's fire alarm system so the door fails safe (unlocks) on a fire signal, and video recording by any panel triggers UK GDPR/Data Protection Act 2018 obligations around signage, retention, and who can access footage. Getting the fire interface wrong is a life-safety issue, not just an inconvenience.

Key Facts

Quick Reference Table

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Symptom Most Likely Cause Where to Check First
No power at panel or monitor at all Blown fuse, tripped MCB/RCD, failed transformer Distribution board, then PSU/transformer output
Panel rings but no audio either way Speaker/mic fault in panel or monitor, or a broken core in a 4+n cable Swap-test panel/monitor if spares available; check cable continuity
Audio works, no video Camera failure, damaged video core, or monitor video input fault Panel camera lens/module first (weather damage common)
Video works, no audio Microphone/speaker fault, separate audio core damaged Panel speaker grille (blocked/corroded) then monitor speaker
Door won't release on command Door strike/maglock power fault, relay failure, or wiring fault to the lock Voltage at the lock terminals during a release command
Works for some flats, not others (communal) Fault at a shared junction or riser cable, not the individual panel Trace from the affected flat back toward the shared distribution point
Picture freezes or drops on IP/Wi-Fi system Network/Wi-Fi signal, router, or provider cloud service issue Signal strength at panel location, router status, provider status page
App shows "offline" but hardware powered Loss of internet at the property, or account/server-side fault Router internet connection, then provider app/service status
Intermittent fault, worse in wet weather Water ingress or corrosion at external panel or cable gland External panel seal, gland, and connector condition
Door release fails specifically at release, not standby Power supply undersized for door strike/maglock current draw PSU rating vs door hardware current draw specification

Detailed Guidance

Power Supply Diagnosis (No Power at All)

Start at the distribution board or consumer unit before touching the intercom itself — a tripped MCB or RCD is a five-minute check that rules out the most common cause. If the circuit is live at the board, follow safe isolation procedure before opening any panel, then check output voltage at the transformer/PSU feeding the intercom. A transformer that's failed completely (no output) needs replacing; one that's producing a low or unstable voltage under load (fine on a multimeter with nothing connected, sagging when the door release is triggered) points to an undersized or failing PSU rather than a wiring fault further along the system.

On communal systems, the PSU is often shared across several flats from a riser cupboard — a single failed shared PSU will present as "several flats' intercoms all stopped working at once," which is a strong diagnostic clue pointing away from any individual flat's wiring.

Audio-Only or Video-Only Faults on 4+n Wire Systems

Because older video door entry systems run audio, video, power and door release on separate cores within one cable, a single damaged core produces a very specific symptom: one function fails while the others keep working. This is one of the most useful diagnostic signals available — if video works perfectly but audio is dead in both directions, suspect the audio core specifically (a nicked cable at a fixing point, a corroded terminal, or a failed component in the panel's audio path) rather than a general power or panel failure.

Where spare panels or monitors are available, swap-testing is faster than continuity-testing every core in a buried cable. Where the cable itself is old, cracked, or has been repeatedly disturbed, factor in that a full cable replacement may be more cost-effective than chasing an intermittent core fault.

Door Release and Lock Faults

A door that won't release on command, when the intercom otherwise rings and communicates normally, is very often a power problem specific to the door hardware rather than the intercom electronics. Electric strikes and maglocks draw meaningfully more current at the moment of release than the intercom draws in standby, and a PSU that's adequately rated for standby can sag below the release threshold under that momentary load — particularly on older installations where a maglock or strike has been added or upgraded without reviewing the PSU rating.

Check voltage at the lock terminals during an actual release command (not at rest) to catch this. Where the door release is integrated with the building's fire alarm system (communal buildings, per BS 7273-4:2015), always confirm the fire override still functions correctly after any intercom repair or PSU change — this is a fire-safety interface, not a convenience feature, and disabling or degrading it during unrelated intercom work is a serious compliance failure.

Network and App Connectivity Faults (IP and Wi-Fi Systems)

On PoE and Wi-Fi-connected intercoms, a "not working" report frequently turns out to be a network fault rather than a hardware fault. Work through:

  1. Is the panel/hub receiving power at all (PoE link light on the switch, or a status LED on a Wi-Fi panel)?
  2. Is the panel/hub connected to the local network (signal strength at a Wi-Fi panel is a common weak point — external panels are often mounted at the edge of Wi-Fi range)?
  3. Is the property's internet connection itself up (router status, other devices on the network)?
  4. Is the manufacturer's cloud service experiencing an outage (check the provider's status page before assuming a local fault)?

Only after ruling out steps 1-4 should you treat this as a hardware fault requiring panel or hub replacement.

Communal / Multi-Dwelling Systems

In blocks of flats, always establish whether a reported fault affects one flat or several before diagnosing. A fault isolated to a single flat's monitor or handset points to that flat's branch wiring or unit; a fault affecting multiple flats simultaneously points to a shared riser cable, junction, or PSU. Skipping this check and replacing an individual flat's monitor when the actual fault is upstream wastes a callout and leaves the underlying problem — and the other affected flats — unresolved.

INTERCOM NOT WORKING — DECISION TREE
│
├─ No power/response at panel OR monitor at all?
│   ├─ Circuit tripped at consumer unit/DB? → Reset once, investigate cause if it trips again
│   └─ Circuit live but no output at PSU/transformer? → Test PSU under load; replace if failing
│
├─ Some functions work, others don't (audio OK/video dead, or vice versa)?
│   ├─ 4+n wire system → Suspect the specific damaged core; swap-test panel/monitor if possible
│   └─ IP/PoE system → Check camera module vs microphone/speaker separately; rarely a cabling
│       issue since all data shares one cable
│
├─ Panel/monitor communicate fine but door won't release?
│   ├─ Voltage at lock terminals during release command low/absent? → PSU undersized or failing
│   │   under load — check rating vs door hardware spec
│   └─ Voltage present but lock still won't release? → Mechanical lock/strike fault, not electrical
│
├─ Affects multiple flats/dwellings at once (communal system)?
│   └─ Trace to shared riser cable, junction box, or shared PSU — do NOT start by replacing
│       individual flat hardware
│
└─ IP/Wi-Fi system, hardware powered, "offline" in app?
    ├─ Panel/hub has network/Wi-Fi signal? → No: relocate or extend Wi-Fi coverage
    ├─ Property internet connection up? → No: fault is the customer's broadband, not the intercom
    └─ Provider cloud service status page shows an outage? → Wait for provider fix, not a site visit

Frequently Asked Questions

Does installing or repairing a video intercom need Building Regulations Part P notification?

Extending or repairing existing low-voltage intercom wiring from an already-compliant supply generally does not require notification. Installing a new dedicated mains circuit or consumer unit way to power the system is notifiable work under Part P and should be self-certified via a competent person scheme or notified to Building Control. If in doubt about a specific job, treat any new circuit from the consumer unit as notifiable.

Why does the video work but the audio doesn't (or vice versa)?

On older 4+n wire systems, audio, video, power and door release each run on a separate core within the cable. A single damaged, corroded, or poorly terminated core takes out only the function it carries, leaving the others working normally — which is why a "video only" or "audio only" fault is a strong clue pointing at that specific core rather than a general system failure. On modern IP systems where everything runs over one data cable, this split is much less common and points instead to a specific hardware module (camera vs microphone/speaker) rather than a cabling fault.

Can I upgrade an old analogue intercom to an IP/video system using the existing cabling?

Usually not directly. Older 4+n wire or two-wire cabling isn't structured data cabling and generally can't carry the bandwidth an IP video intercom needs; most IP upgrades require running new CAT5e/6 cable to the panel location, even if the existing conduit route can be reused to pull the new cable through.

Who is responsible for fixing a communal intercom fault — the landlord, managing agent, or individual flat owner?

This depends on the lease and the specific fault. Faults in the shared parts of the system (the external panel, riser wiring, shared power supply) are typically the landlord's or managing agent's responsibility as part of the building's common parts; a fault isolated to an individual flat's internal handset or monitor is more often the leaseholder's or tenant's responsibility. Tradespeople should confirm who is instructing (and paying for) the work before diagnosing, particularly where a fault turns out to be shared-parts rather than flat-specific.

Does recording video at the door trigger GDPR obligations?

Yes. Any video intercom that captures and stores images — even a few seconds around each visitor — makes whoever controls the system a data controller under UK GDPR and the Data Protection Act 2018. This applies to both single dwellings (subject to a limited "domestic purposes" exemption that narrows significantly for communal buildings) and blocks of flats, where clear signage, a defined retention period, and a documented process for who can access footage are expected good practice.

Regulations & Standards