Ama-Drainer 301C Pump: A Surprisingly Simple Fix⌗

My Ama-Drainer 301C pump is installed in a KSB Box Mini—probably the kit your plumber installs for washing machines or small sinks that sit below the household waste line. Normally, you’d think this thing has an easy life… until it doesn’t.

After my sump overflowed three times, I had cleaned the pump it worked after a good clean everytime, I finally called the plumber in the hope to use my building warranty to have it replaced. He checked a few things:

  1. The pump was installed well within spec and had plenty of power.
  2. The unit itself looked fine—clean, not clogged—but some dirt might have temporarily blocked the mechanism.

The annoying part? While the plumber was there, the pump worked perfectly. One hour later, it stopped again. He basically shrugged and suggested a replacement. I started thinking about whether to get a bigger 303 pump or a cheaper Jung unit, measuring what fits in my box etc…

The DIY Fix⌗

Before spending money on a new pump, I looked online for repair tips and stumbled across this old post from 2014:
Haustechnikdialog – Ama-Drainer 301/2 schaltet nicht mehr ab

Turns out, the fix is ridiculously simple. The pump has a floater that lifts a small cam, which moves a magnet in front of a sensor (either a Hall effect sensor or a reed switch). Over time, dirt can slightly misalign it. In my pump, the activation level had dropped by about 3 cm—marked by a little dirt line.

I just cleaned the mechanism and added two small circular 2mm thick magnets in front (one 6x2mm and one 8x2mm). I think there’s plenty of space, you can fit a 3mm wide easily. Boom—the pump started working again, just like new. No expensive replacement needed, no fancy tools, just a bit of patience.

fix

Good luck fixing your pump!