Timer behaving as the wrong type (on-delay vs off-delay)
The timer switches at the wrong point in the sequence because it's acting as the wrong function — on-delay where off-delay is needed, single-shot where cyclic is needed, and so on.
Safety first
A timer in the wrong mode can energise or hold equipment unexpectedly. Confirm the intended behaviour is safe before and after changing the mode.
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
Function/mode selector set wrong
Most likelyMulti-function timers have a mode selector; the wrong selection gives on-delay vs off-delay vs interval behaviour.
- 2
Wrong timer type fitted
#2A fixed-function timer of the wrong type was installed for the application.
- 3
Trigger/supply wiring matched to a different mode
Least likelySome modes need the supply/trigger wired differently; mismatched wiring gives unexpected behaviour.
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.
Confirm what behaviour the sequence needs (on-delay, off-delay, interval, cyclic).
A clear required behaviour.
Requirement clear — check the mode selector against it.
If unclear, confirm the intended behaviour from the control description.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Timer wrong mode
→ step 2 - 2decision
Is the required behaviour (on/off-delay/interval) clear?
Yes→ step 3No→ step 4 - 3decision
Does the mode selector match the requirement?
Yes→ step 5No→ step 6 - 4result
Confirm intended behaviour from the control description.
- 5decision
Does the supply/trigger wiring suit that mode?
Yes→ step 7No→ step 8 - 6result
Set the correct mode (or fit the right fixed-function type).
- 7result
Re-test the sequence.
- 8result
Rewire per the timer's diagram for that mode.
Common mistakes apprentices make
- Not checking the multi-function mode selector.
- Fitting a fixed-function timer of the wrong type.
- Wiring the supply/trigger for a different mode than selected.
- Changing the mode without confirming the intended behaviour.
When to stop & escalate
If the intended timing behaviour isn't documented, confirm it against the control description before changing the mode, especially where it affects start/stop sequencing.
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
Timer relay not switching its output
A timer relay is powered but its output contact never changes state — the delayed action (start, changeover, stop) never happens, or it switches at the wrong time.
Timer times out too long or too short
The timer switches, but at the wrong time — the delay is much longer or shorter than it should be, throwing out the sequence.
Star-delta starter not transitioning to delta
A star-delta (wye-delta) starter starts the motor in star but never switches to delta — the motor runs weak/slow, or trips, because it stays in the starting connection.
Learn the theory
How the gear and circuits behind this fault actually work.