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Fault Finder
DIAGNOSTICS

Fault-Finding Guide

A structured sequence for common fire alarm faults. Isolate safely and preserve system coverage wherever possible.

Open-circuit / loop break
  1. Confirm the exact loop/zone fault and note panel messages before resetting.
  2. Check whether both loop ends are visible at the panel and whether isolators have operated.
  3. Inspect recent works, junctions, bases and interfaces first.
  4. Split the circuit methodically and meter only where permitted by the equipment manufacturer.
  5. Restore devices, verify communication and complete a functional test.
Short-circuit / isolator operated
  1. Identify operated isolators or the isolated loop section from panel diagnostics.
  2. Inspect for damaged cable, trapped cores, reversed terminations, water ingress and failed field devices.
  3. Disconnect sections only in accordance with the panel/device instructions.
  4. After rectification, confirm isolators reset and all expected addresses return.
Earth fault
  1. Confirm whether the fault is positive-to-earth or negative-to-earth if the panel reports this.
  2. Disconnect external circuits in a controlled sequence to identify the affected circuit.
  3. Check screened cable terminations, damp equipment, gland entries, damaged insulation and ancillary interfaces.
  4. Do not megger connected electronic fire alarm devices unless the manufacturer expressly permits the test and equipment is safely disconnected.
Missing / unexpected / duplicate device
  1. Compare panel configuration with the as-fitted loop schedule.
  2. Check device address card/DIL setting and base seating.
  3. Check for duplicate addresses after replacement or extension works.
  4. Check protocol compatibility and whether a combined device consumes more than one address.
Battery / charger fault
  1. Check battery age, visible damage, terminals and fuse protection.
  2. Measure charger output and battery voltage using the manufacturer’s procedure.
  3. Confirm configured battery capacity is compatible with the panel/PSU charger.
  4. Replace batteries as matched sets where required and record the date.
Intermittent communications / noise
  1. Look for loose terminations, high resistance joints and intermittent shorts.
  2. Confirm cable type, segregation, screen/earth arrangement and manufacturer wiring rules.
  3. Check device load and voltage at the remote end under the relevant operating state.
  4. Use manufacturer diagnostic/test equipment where available.