Help me find out what this component is

Hello everyone,
I need some help to find out what is this little piece that every three or four months decide to burn. :wall::wall:
It's mounted on a controller for a water valve, that's made for cleaning the pipes releasing a big amount of water from the pipes themselves.
The circuit have a power supply that brings 12 volts alternate current and before getting converted to direct current it pass from this little piece: what can it be? :confused:
Attachment 4226
Attachment 4227