ApprenticeLow risk

Motion-sensor light not working correctly

A sensor (PIR) light won't come on, stays on permanently, or triggers at the wrong times — common on eaves, garages, and entries.

Start fault-finding

Safety first

Isolate before adjusting or replacing the fitting. Outdoor fittings should be weatherproof — check seals when working on them.

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.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

1
Mode / settings wrong (test, time, lux)
Most likely
Many PIR lights have test/auto modes, on-time, and daylight (lux) settings that, set wrong, cause odd behaviour.
2
Sensor aimed/located poorly
#2
Wrong aim or range means it misses movement or triggers on traffic/animals.
3
Daylight cut-off active
#3
Set to night-only, it won't activate in daylight (working as intended) — or the lux setting is wrong.
4
Faulty sensor or lamp
Least likely
The PIR head or the lamp has failed.

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.

Test 1 of 3

Check the mode and settings (test mode, on-time, lux/daylight) match what you expect.

Expected reading

Settings consistent with the desired behaviour.

Your actual reading

If it passes

Settings fine — check aim/range and the lamp/sensor.

If it fails

Wrong mode/settings — set them correctly and re-test.

Often leads toOutdoor / garden light not working A single light not working

View all expected readings at once

1. Check the mode and settings (test mode, on-time, lux/daylight) match what you expect.

Settings consistent with the desired behaviour.

2. Check the sensor's aim, range, and that the daylight cut-off isn't preventing daytime testing.

Sensor covers the right area; tested in suitable light.

3. Isolate and test the lamp and sensor head (swap/replace as needed).

Working lamp and responsive sensor.

Fault-finding flowchart

The same logic as a decision tree.

1
start
Sensor light faulty
→ step 2
2
decision
Are mode and settings (time/lux) correct?
Yes→ step 3No→ step 4
3
decision
Is the aim/coverage right (and tested in suitable light)?
Yes→ step 5No→ step 6
4
result
Set the correct mode/settings and re-test.
5
decision
Do the lamp and sensor head test healthy?
Yes→ step 7No→ step 8
6
result
Re-aim/relocate the sensor.
7
result
Re-verify settings/aim.
8
result
Faulty lamp/sensor — replace.

Common mistakes apprentices make

Testing in daylight when the lux setting blocks daytime operation.
Leaving it in test mode (short on-time) and thinking it's faulty.
Poor aim so it misses the intended approach.
Replacing the fitting before checking the settings.

When to stop & escalate

Replacement and any wiring is licensed electrical work. Persistent false triggers from a fundamentally poor location may need the fitting repositioned.

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.

Related faults

Outdoor & garden

Outdoor / garden light not working

An outdoor or garden light is out — could be the lamp, a sensor/timer, weatherproofing/water ingress, or the supply.

4 causes2 test steps

ApprenticeMedium risk

Lighting

A single light not working

One light fitting is dead while the rest of the lights on the circuit work fine — points at the lamp, the fitting, or the switch for that point rather than the whole circuit.

4 causes3 test steps

ApprenticeMedium risk

Outdoor & garden