Commercial exhaust / ventilation fan not running
A larger exhaust/ventilation fan (carpark, kitchen, plant room) won't run — pointing at its starter/control, supply, motor, or an interlock with a control system.
Safety first
Larger fans are often three-phase on a starter and may be safety/ventilation-critical (e.g. carpark CO, kitchen exhaust). Isolate and prove dead; confirm the system's role before disabling anything.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Starter/control not energising the fan
Most likelyThe fan's contactor/starter isn't being commanded (control circuit, overload, or interlock).
- 2
Overload tripped / motor fault
#2The fan's overload has tripped or the motor has a fault.
- 3
Control-system interlock holding it off
#3A BMS/CO/fire interlock is holding the fan off (possibly correctly).
- 4
Supply / single-phasing
Least likelyLost supply or a lost phase on a three-phase fan.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeCheck whether the fan's starter/contactor is being commanded and whether its overload has tripped.
Starter commanded; overload not tripped.
Commanded — check the motor and supply.
Not commanded / overload tripped — trace the control/overload (see motor faults).
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Commercial fan not running
→ step 2 - 2decision
Is the starter commanded and the overload not tripped?
Yes→ step 3No→ step 4 - 3decision
Is any safety/BMS interlock NOT holding it off?
Yes→ step 5No→ step 6 - 4result
Trace the control/overload (see motor fault-finding).
- 5decision
Is the motor healthy and three-phase supply balanced?
Yes→ step 7No→ step 8 - 6result
An interlock holds it — confirm whether that's correct first.
- 7result
Re-check the control/starter.
- 8result
Motor fault or single-phasing — rectify.
Common mistakes apprentices make
- Defeating a safety/ventilation interlock without understanding its role.
- Not checking the overload.
- Overlooking single-phasing on a three-phase fan.
- Assuming the motor before checking the control/starter.
When to stop & escalate
Ventilation fans tied to safety systems (carpark CO, smoke/kitchen exhaust) must not be defeated — confirm the system design. Starter/motor/three-phase work is licensed electrical.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
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Related faults
Bathroom/laundry exhaust fan not working
An exhaust fan won't run, runs weakly, or keeps running — common causes are the switch/timer, a seized/dusty motor, or supply.
Motor overload keeps tripping
The thermal/electronic overload trips repeatedly, either on start or after the motor has run for a while. Resetting only buys you a short run before it trips again.
Three-phase equipment single-phasing (lost a phase)
Three-phase equipment is misbehaving — motors humming, struggling, overheating, or tripping — because one phase has been lost somewhere between the supply and the load.