This is an electric water-pump controller


There is a component that I don't know what it is. it's marked as "RD". look:


In your opinion What would it be?

  • \$\begingroup\$ You appear to have not shown a component that is important. Is a moving magnet near the RD component when the PCB is in operating position? If so, what moves the magnet? \$\endgroup\$
    – Russell McMahon
    Apr 8, 2016 at 15:28

1 Answer 1


Definitely a reed relay switch (no coil). You can even see the thin metal contacts.

  • \$\begingroup\$ Yeah - i'm guessing there's a fixed magnet attached to some part of this device that aligns with it. \$\endgroup\$ Apr 8, 2016 at 6:15
  • \$\begingroup\$ Or the reed switch is monitoring a float with magnet to prevent applying power to the heater if the water level is not high enough? \$\endgroup\$
    – Transistor
    Apr 8, 2016 at 6:16
  • 2
    \$\begingroup\$ I'd say reed switch, rather than reed relay - I don't see any sign of a relay coil. The switch would be operated by a magnet that moves near the board. \$\endgroup\$ Apr 8, 2016 at 6:31
  • 1
    \$\begingroup\$ I have seen this used to turn on special diagnostics / setup modes. \$\endgroup\$
    – Spoon
    Apr 8, 2016 at 6:31
  • \$\begingroup\$ @PeterBennett: Agreed. \$\endgroup\$ Apr 8, 2016 at 6:40

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