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Do It Yourself - Fixing a Shower Sump on Your Boat

Several months ago, I noticed the shower drain in my boat was not removing water as it should. Rather than water running down the drain, it just collected in the pan at the bottom of the shower. Recently, I decided to tackle the job and figure out what was going on. I knew I was going to spend the entire July 4th weekend on the boat and I wanted to be able to take a shower without worrying about the water building up.

If you are not familiar with the workings of a basic shower sump system on a boat, it is actually pretty simple. The drain at the bottom of the shower empties into a box down in the bilge. Since the box is most likely below water level, there is a pump in the box that pumps the water up, out and overboard. Often the pump has a float switch attached to it to cycle the pump on when the water gets to a certain level and off when the box it empty.

A Basic Sump Pump Setup

In my case, I had already checked the line from the shower drain to the box and verified that it was not clogged. Based on that, I figured that the pump must not be working for some reason. I have an older boat and I think that the shower sump pump is probably the original one so I was assuming that it needed to be replaced. I started by removing the small hatch in the sole (That’s the floor for you landlubbers) that allows me to access the shower sump. Using a screwdriver, I removed the 4 cover screws and the cover on the box revealing the pump inside. Given that it had not been working, the first thing that I had to do was remove the water. This was easily done with a plastic cup and a bucket.

I flipped the sump pump switch in the shower to the on position and then went back to the box and manually manipulated the float switch to see if the pump would come on. It did not. So far, my theory of a bad pump was correct.

Open Sump Box.  The top of the pump (blue) can be seen with the black float switch connected to the side.

The next thing I needed to do was verify that power was actually getting to the system. To do so, I cut the power feed coming from the switch in the shower. I made sure to cut the wires just outside of the box as all of the wiring inside the box is sealed and I did not want to disturb that. After turning the switch on in the shower, I used a voltage tester to test for 12 volts at the pump and got a reading of 12.42 volts. At this point it was still looking like a bad pump.

With the switch on. the circuit showed 12.42 volts.

Using a screwdriver, I removed the float switch and twisted the pump cartridge out to remove the pump assembly. I cut the wires between the float switch and the pump and then hardwired the pump directly to the wiring coming from the shower switch. Once again, I flipped the switch and the pump came on! It was clearly apparent the the problem was the float switch and not the pump.

I grabbed the float switch and headed to West Marine. I was sure that they would have one in stock, especially since the old one had a West Marine sticker on it. Unfortunately, they did not have it. It was not because my local West Marine store did not stock their store well but because that float switch was so old that it is no longer manufactured.

Old float switch after removing from pump.

I now had two options:

1. Replace the entire sump box assembly including pump and float switch. The existing box was molded to fit the existing float switch and pump. None of the switches and/or pumps I found would fit the box without having to drill new screw holes in the box. This would most likely result in a leaky sump box.

2. Forget the float switch and hard wire the motor to the switch on the shower panel. This would be much easier (and cheaper) but the pump would always be running when the panel switch is turned on regardless of whether there is water in the box or not.

By removing the float switch, the pump will be controlled solely by the switch on the shower panel.

I installed the pump back into the box without the float switch and hard wired it to the circuit from the panel switch in the shower. My thought was that you could simply flip the switch on when you turn on the shower and flip it off again when done. After buttoning everything back up, I ran the shower until a couple of inches of water built up in bottom of the shower pan. I then flipped on the pump switch and watched it all run out. Success!!!

Sump pump reinstalled without the float switch

Including my run to West Marine, the entire project took me about an hour and a half to complete and ultimately cost me nothing except for a few cents for new wiring connectors which I already had on board. The next weekend, I enjoyed my showers on the boat without having to scoop water out of the shower pan afterwards. Truly a Win-Win situation. The next time you have something that stops working on your boat, think about tackling it yourself. It may not be as hard as you think.

Happy Boating

Capt. Frank

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  1. Sounds complicated. You have the know how! I will just take ours in to an mechanic! Great article though! :)

  2. You can get rocker switches that you have to hold on and switch off when you let go. Stops you accidentally leaving the pump on.

  3. Nicely done Cap'n! I'll help ya look fer a replacement float that'll fit when (or if) ya ever wanna... ��

  4. I too have an older boat with a Shower sump. After my bilge pump float switch failed, I got to thinking about the Shower sump. The weak link being the float switch. My mind is not as sharp as it used to be and I can forget to turn off the pump after use. To back check myself i installed a mechanical timer switch with a max run time of 1/2 hour. Works Great!


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