Introduction to the MxPro 5

The Advanced MxPro 5 is one of the most widely deployed fire alarm panels in the UK commercial market. It's a flexible, networked addressable panel supporting multiple loop protocols (Protocol 80, Apollo XP95, Hochiki ESP, and others) and scaling from single-panel to large multi-panel networked installations.

Because of its flexibility, it's also a panel that generates a distinctive set of fault conditions — some specific to its architecture, some common to addressable systems in general. This guide covers the faults you're most likely to encounter on site, and the diagnostic approach for each.

Network Faults

The MxPro 5 is designed to operate as part of a networked system, and network faults are among the most disruptive issues you'll encounter. They can take entire zones or panels offline.

Symptoms

Panel displaying "Network Fault" or "Node Fault"
Other panels on the network showing as offline from the affected panel's perspective
Devices on remote panels appearing as faults
Network status LED showing fault condition

Probable causes

Network cable break — The most common cause. The MxPro 5 network uses dedicated network cabling (typically RS485 or the Advanced proprietary network protocol). A break between any two nodes takes out communication with all nodes beyond the break.
Faulty network card or module — The network interface card in the panel can fail, presenting as an inability to communicate even when the cable is intact.
Incorrect network addressing — If a panel has been configured with a duplicate network address (common after replacement or reconfiguration), the network will fault.
Termination resistor missing or incorrectly placed — RS485-type networks require termination resistors at the two physical ends of the network run. Missing or misplaced termination causes reflections that disrupt communication.

Diagnostic approach

First, establish which node or nodes are reporting faults and which are unreachable. The MxPro 5's network diagnostics screen (accessed via the panel menu) will show the communication status of each node.

If a single node is unreachable, check the cable between the last communicating node and the unreachable node. If multiple nodes are unreachable, the fault is likely upstream of all of them.

Check the physical network connections at each panel: network card seating, cable terminations, and termination resistor placement. If you have access to network diagnostic tools, check the RS485 bus voltage and look for evidence of a short or open on the network cable.

Loop Faults

Ground/Earth Faults

Symptoms: Panel showing "Earth Fault" or "Ground Fault" on a specific loop.

A ground fault means one of the loop conductors has a path to earth, usually through damaged cable insulation. The MxPro 5 actively monitors loop insulation and will generate a fault as soon as it detects this condition.

Diagnostic approach:

Note the loop number
Disconnect the loop at the panel — if the fault clears, the fault is in the field wiring or a device
Use a megohmmeter to measure insulation resistance between each loop conductor and earth. Look for resistance below the minimum acceptable level (typically >1 MΩ in good condition, though the panel will fault at much higher resistance values in some configurations)
Section the loop using isolator modules to narrow down which section the fault is in
Walk the route inspecting cable — look for damage, pinch points, cable touching metalwork

Common locations: Cable trays where cable has been bent sharply, entries to trunking or conduit, device bases where a cable core has been overtightened against the panel earth.

Short Circuit Faults

Symptoms: "Loop Short Circuit" fault, possibly with a section of devices going offline.

On the MxPro 5, short circuit faults should be automatically isolated by the isolator modules (EN 54-17 compliant isolators on Protocol 80 loops). The panel will show which section of the loop is isolated.

Diagnostic approach:

Identify the isolated section from the panel display
Disconnect devices in that section one at a time to identify the device or cable causing the short
Check device bases — a cracked base or a foreign object inside the base can cause a short
Check cable condition in the isolated section

Communication Loss Faults

Symptoms: Specific devices showing as "Communication Lost" or offline, but loop otherwise operational.

This indicates the panel can't communicate with specific devices, even though the loop is generally intact. Common causes:

Device removed from base without shorting plug
Failed device (detector head failure)
Addressing conflict (duplicate addresses — will cause both devices with the same address to disappear)
Device outside the supported address range for this loop type

PSU (Power Supply) Faults

Mains Supply Fault

Symptoms: "Mains Fault" displayed on panel.

The panel has lost its 240V mains supply. Check:

MCB or fuse feeding the panel hasn't tripped
Mains supply present at the panel's mains input terminals
Mains wiring connections at the panel haven't come loose

Battery Fault

Symptoms: "Battery Fault" or "Battery Low"

The panel's standby batteries are below the minimum voltage threshold, or the batteries have failed. The MxPro 5 monitors battery health and will alert well before batteries reach a state where they'd fail to provide the required standby duration.

Check:

Battery voltage with a multimeter (typically 2 × 12V sealed lead-acid). A battery showing significantly below 12V at rest is likely failed.
Battery age — sealed lead-acid batteries used in fire alarm panels should be replaced typically every 4 years, depending on usage and environment.
Charger circuit — if both batteries show low voltage simultaneously, the charger may have failed.

Charger Fault

Separate from battery fault — indicates a problem with the charging circuit. Requires investigation of the PSU board.

Accessing Fault Information on the MxPro 5

The MxPro 5 provides detailed fault logging and status screens:

Fault log: Access via panel menu > Faults. Shows current active faults with timestamps.
Device status: Panel menu > Devices. View communication status for individual devices.
Network status: Panel menu > Network. View node communication status.
Event log: Panel menu > Events. Full history of alarms, faults, and operator actions.

When attending a fault, always check the event log. The fault history will often show a pattern — repeated fault/restore cycles before the current fault — that helps identify intermittent issues before they become persistent faults.

Documentation

Per BS 5839-1:2025, all faults, investigations, and remedial work must be documented in the system log book. For MxPro 5 systems, include:

Fault type and panel address
Date and time attended
Probable cause identified
Remedial action taken
Confirmation of system restoration

Attending an MxPro 5 fault right now? Sign up to Incognito F&S and ask the AI assistant — describe the fault and get a structured diagnostic response tuned to the Advanced MxPro 5 in under 30 seconds.

Advanced MxPro 5: Common faults and how to clear them