Troubleshooting Guides · Free Tool

Gas Detector Fault Finder

Choose what the gas detector is doing and get likely causes for catalytic, infrared and electrochemical detectors, with checks and fixes.

Fails bump testZero driftFalse alarmsOptics fault

What do you see?

SymptomReads low on bump test

Most likely causeCatalytic sensor poisoned (silicones, sulfur, lead)

First checkLow response after cleaning

Cause	How to check	Fix
Catalytic sensor poisoned (silicones, sulfur, lead)	Low response after cleaning	Replace sensor; find source of poisons
Blocked sinter or weather guard	Inspect and clean	Clean or replace guard
Wrong test gas or flow	Check cylinder and regulator	Use correct gas and flow

Before You Start

Work under a permit, inform the control room and put the loop in manual or bypass the trip before touching a live instrument.
Inhibit the detector with operations approval and keep the inhibit time short.
Use in date, certified test gas of the correct type.
Check the sensor installation date against its service life.

Likely cause	How to check	Fix
Catalytic sensor poisoned (silicones, sulfur, lead)	Low response after cleaning	Replace sensor; find source of poisons
Blocked sinter or weather guard	Inspect and clean	Clean or replace guard
Wrong test gas or flow	Check cylinder and regulator	Use correct gas and flow

Likely cause	How to check	Fix
Zeroed in contaminated air	Zero with zero gas	Rezero correctly
Sensor ageing	Drift increasing over time	Replace sensor
Temperature or humidity swings	Correlate with weather	Check compensation; fit guard

Likely cause	How to check	Fix
Cross sensitive gases or vapours	Check process activities nearby	Relocate or choose different sensor
Steam or water on sensor	Check environment	Fit splash guard
Radio interference	Alarm when radios used nearby	Improve shielding; keep radios away

Likely cause	How to check	Fix
Dirty or wet optics	Inspect windows	Clean; fit hood
Open path misaligned	Check alignment signal	Realign
Heavy fog or obstruction	Check path	Accept temporary loss or relocate

Likely cause	How to check	Fix
Inhibit left on	Check fire and gas system status	Remove inhibit
Loop or power fault	Measure current	Repair wiring or supply
Detector fault output	Check detector status	Repair or replace

Key insight: a bump test proves the detector sees gas; only a calibration proves it reads the right amount.

How often should detectors be bump tested?

As set by the site and maker; often monthly to quarterly for fixed detectors, with calibration at longer intervals.

Why do catalytic sensors fail low?

Poisoning or inhibition reduces their response, which is dangerous.

Can IR detect hydrogen?

No; hydrogen needs catalytic, electrochemical or other sensor types.

Hazardous area classification zones

A practical, field focused guide on instrumentationblog.in that explains the theory behind this tool and how engineers apply it on real plants.