IP Intercom Not Connecting: How to Troubleshoot Door Stations and Monitors

An IP video intercom has more parts than it looks: an outdoor door station with a camera and call button, one or more indoor monitors (or indoor stations), a network switch, often a phone app and cloud service, and an electric lock with its own power supply. When "the intercom is not working", any of these can be the cause.

This guide is vendor-neutral. The examples use terms you will see on common systems: Hikvision calls its units door stations and indoor stations and uses the Hik-Connect app, while Dahua calls them VTO (outdoor) and VTH (indoor) units and uses the DMSS app. Menu names vary by model and firmware, so check your manual for the exact path.

Symptoms

Likely causes

1. No or insufficient PoE. The switch port does not supply PoE, the budget is exhausted, or a passive injector is used with a standard device.
2. Network or VLAN mismatch. The door station and monitors are in different subnets or VLANs, so they cannot find each other.
3. Changed IP addresses. Devices on DHCP got new addresses after a power cut, and the monitor still points to the old one.
4. Wrong linking or numbering. The indoor monitor's room number or the door station address does not match what the door station is configured to call.
5. SIP not registered. Wrong server address, extension or password, or the router interfering with SIP traffic.
6. App or cloud account issues. The device is bound to an old account (the previous tenant or the installer), the cloud service is disabled, or the phone is blocking notifications.
7. Lock power or relay. The lock's power supply has failed, the relay is wired to the wrong terminals, or the relay is being asked to carry more current than it is rated for.
8. Weather and corrosion. Water in the door station or its cable, especially on exposed façades near the sea.

Safe checks you can do

1. Check the door station lights and screen. Is it powered? Does the camera show on the indoor monitor's live view?
2. Check the switch. Is the door station's port light on? If the switch has a PoE indicator, is it lit for that port?
3. Test one direction at a time. Call from the door to the monitor, then use the monitor's live view of the door. If live view works but calls do not, it is configuration, not cabling.
4. Note what changed. A new router, a power cut, a new tenant, a phone change or building work.
5. On the app, check whether the device shows online, and whether notifications are allowed for the app in the phone's settings.
6. Test the lock separately. Most systems have an unlock button on the indoor monitor and an exit button inside the door. If the exit button opens the door but the intercom does not, the problem is the relay or its wiring. If neither works, it is the lock or its power supply.

Warning Lock power supplies are usually connected to mains electricity. Do not open the power supply, the door station's back box or the lock wiring while it is powered. Leave mains connections to a qualified electrician.

Warning If a door is on a fire escape route, do not bypass, disconnect or wedge the lock to "fix" it. Escape doors must open safely in an emergency. Call a professional.

Solutions

Power and PoE

• Confirm the switch supports the same PoE standard as the door station (usually IEEE 802.3af or 802.3at). Check the datasheet.
• Do not use passive PoE injectors with standard 802.3af/at devices unless the manufacturer says it is safe. The wrong voltage can damage them.
• Check the switch's total PoE budget. Indoor monitors with screens and door stations with heaters or bright lights add up. Our PoE budget calculator does the sums.
• Keep cable runs within 100 metres and use solid-copper cable.
• Put the PoE switch on a UPS so the intercom keeps working during short power cuts.

Network and VLAN mismatch

Door stations and indoor monitors normally need to be in the same subnet to call each other directly, unless the system is designed to route between networks.

• Check each unit's IP address, subnet mask and gateway. They must all be in the same range. Our IP subnet calculator helps.
• If your network uses VLANs (for example a separate VLAN for security devices), make sure every port used by the intercom is in the same VLAN. A port left on the office or guest VLAN is a common mistake after a switch replacement.
• Give each unit a fixed IP address, or a DHCP reservation on the router, so addresses do not change after a power cut.
• If two devices have the same IP address, change one. On Hikvision systems the SADP tool lists devices and their addresses. Dahua provides a similar device configuration tool.

Linking and numbering

Most systems link the indoor monitor to the door station by entering the door station's IP address on the monitor, and assign each monitor a room or apartment number. The call button on the door station is set to call that number.

• Check that the door station address saved on the monitor is current.
• Check that the room number on the monitor matches the number the button or keypad calls.
• In multi-unit buildings, check that two monitors do not share a number by mistake.
• Make sure the door station and monitors run compatible firmware versions. Update the door station and monitors together, using files from the manufacturer's official site.

SIP registration

If the intercom calls SIP phones, a PBX or a hotel phone system, the door station must register with the SIP server.

1. Open the door station's SIP settings and check the registration status. It should say registered.
2. Check the server address, port (SIP normally uses 5060), extension number, authentication user name and password against the PBX. A single wrong character prevents registration.
3. Check the PBX side: the extension exists, is enabled and is not already registered to another device.
4. If the PBX is across the internet or another network, firewalls and NAT can block or break SIP. Many routers have a "SIP ALG" feature that rewrites SIP traffic and often causes failed registrations or one-way audio. Turning it off is a common fix, but check with whoever manages the router first.
5. No audio or one-way audio usually means the media (RTP) traffic is blocked, or the units do not share a common audio codec.

App and cloud account

• The door station (or the indoor monitor, depending on the system) must have its cloud service enabled, with working gateway and DNS settings, to reach the app.
• Find out whose account the device is bound to. If a previous tenant, owner or installer still has it, they may receive your calls, and you cannot add it. Follow the manufacturer's procedure to unbind it, which may need the installer or the device's verification code.
• Use device sharing to give family or staff access, rather than sharing one login.
• On the phone, allow the app's notifications and turn off battery optimisation for it. Android battery savers often stop call alerts arriving.
• Update the app and log in again.

Plays from YouTube when you press play.

Door lock relay and power

On most door stations the lock relay is a dry contact: a switch with terminals usually marked NO (normally open), NC (normally closed) and COM (common). It switches the lock's power on or off. It does not supply power itself, unless your manual says the unit can power a small lock directly.

• Electric strikes are usually fail-secure: they unlock when powered. Wire them through NO and COM.
• Magnetic locks are fail-safe: they hold when powered and release when power is cut. Wire them through NC and COM.
• Check the lock's power supply output with the installer. A failed supply or a flat backup battery is a common cause.
• Check the relay's current rating in the manual. If the lock draws more, use a separate relay or an access control power supply.
• DC locks should have a protection diode across the coil (many come fitted) to protect the relay contacts.

Warning Magnetic locks on exit doors need a safe release method, such as an exit button and an emergency break-glass, according to local fire safety requirements. Do not change how an escape door locks without professional advice.

Weather, coast and heritage façades

Outdoor door stations face sun, rain and salty air. Use a rain hood or recess where possible, seal cable entries, and check the unit's IP rating suits the location. In Stone Town, a UNESCO World Heritage Site, visible changes to building façades need approval from the conservation authority. Plan discreet units and cable routes, and check with the authority before mounting anything outside.

When to call a professional

Call a professional if the door station is dead after checking power, the system uses SIP with a PBX, the lock or its power supply needs attention, the device is bound to an account you cannot access, or the door is part of a fire escape route. Before calling, collect:

• Brand and model of the door station and indoor monitors, with firmware versions.
• Photos of the switch port lights and of any error on the monitor.
• IP addresses of each unit, if you can see them.
• The SIP registration status screen, if SIP is used.
• The app's error message and which account the device is in.
• The lock type (strike or magnetic) and whether the exit button works.
• What changed recently: router, power cut, tenant, phone.

Frequently asked questions

When to call Extrion

Extrion Tech installs and supports IP video intercoms, access control, door locks and the networks they run on. See our security auditing and implementation service or contact us with your intercom model and a description of the fault.

This guide is general information to help you plan. Prices, product features and regulations change, so confirm the details for your own site before you buy.

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