Fix: relay clicks but the load does not switch
The relay coil works but the contacts do not carry the load: wrong NO/NC terminal, loose screw terminal, or a load beyond the contact rating.
Community draft — report a mistake
What you see
Relay ON (click)
Relay OFF (click)
— lamp / pump does not reactRelay ON (click) Relay OFF (click) — lamp / pump does not react
A clicking relay means the board and coil side are fine. The problem is on the contact side, which is often connected to mains voltage — switch off at the MCB before touching any terminal.
Quick fix — try in order
- 1
Use COM and NO for “on when energised”
NO (normally open) closes when the relay clicks on. Wiring to NC does the opposite.
- 2
Check the screw terminals
Loose or partly stripped wires are common; tighten and tug-test them (power OFF first).
- 3
Check the load rating
Relay modules are rated for resistive loads (e.g. 10 A 250 V AC). Motors and pumps need a contactor; the relay should only switch the contactor coil.
- 4
Test the contacts with a multimeter
With everything unpowered from mains, check continuity between COM and NO while the relay is on. No continuity = burnt contacts.
Why it happens
Clicks but nothing happens
The click proves the coil side works. The fault is on the contact side: wiring, terminal, or welded/burnt contacts.
Contacts burnt by a motor
Motor start-up current can weld or pit relay contacts. Use a contactor rated AC-3 for pumps and motors.
Active-LOW modules
If the relay is on when your code says off, the module is active-LOW; invert the logic in code.
Board-specific notes
Mains safety: Anything at 230 V must be wired by an electrician with the circuit off at the MCB. See the relay module page.
Parts: Relay module — pinout, voltage and library notes.
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