Timer output chatters or pulses at changeover
When the timer reaches its set point, the output chatters or pulses instead of switching cleanly, causing the downstream device to buzz or operate erratically.
Safety first
A chattering output can make a contactor downstream chatter and arc. Don't leave it running in that state; isolate to investigate.
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
Marginal supply to the timer
Most likelyA weak supply that sags as the output switches causes the timer to hover at the threshold and chatter.
- 2
Downstream load too large for the timer contact
#2An output contact switching too heavy a load can struggle and bounce.
- 3
Failing timer / worn contact
#3An aging timer's output contact can bounce or chatter near end of life.
- 4
Feedback/interaction in the circuit
Least likelyThe switched load affects the timer's own supply/trigger, creating an oscillation.
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.
Watch the timer's supply as the output switches — does it sag/fluctuate at changeover?
Steady supply through the switching event.
Supply steady — check the load size and the timer itself.
Supply sags at switch — strengthen/stabilise the supply.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Timer output chatters
→ step 2 - 2decision
Does the timer supply stay steady at changeover?
Yes→ step 3No→ step 4 - 3decision
Is the downstream load within the contact rating?
Yes→ step 5No→ step 6 - 4result
Supply sags — strengthen/stabilise it.
- 5decision
Does a known-good timer switch cleanly (no feedback)?
Yes→ step 7No→ step 8 - 6result
Load too large — interpose a suitably rated relay.
- 7result
Original timer worn — replace it.
- 8result
Circuit feedback — separate the timer supply from the switched load.
Common mistakes apprentices make
- Switching a heavy load directly on a small timer contact.
- Ignoring a supply that dips when the output operates.
- Not trying a known-good timer to confirm a worn contact.
- Missing a feedback interaction between the load and the timer supply.
When to stop & escalate
If the supply is marginal across several control devices, review the control supply. For heavy loads, use a properly rated interposing relay as standard practice.
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.
Contactor chattering or buzzing instead of holding in
The contactor rapidly clicks/buzzes, pulls in and drops out repeatedly, or hums loudly without seating cleanly. Often comes with arcing noise and heat.
Control relay coil not energising
A plug-in or interface relay isn't picking up — its indicator stays off and its contacts don't change, so whatever it controls never operates.