A shower aboard is one of the best parts of cruising, right up until the sump stops draining and you are standing in a tray of soapy water. Shower sump pumps fail more than almost any other pump on a boat, mostly because they spend their lives pumping warm water full of hair, soap scum and body oils.

Quick answer: most shower sump failures come down to five things: a stuck or fouled float switch, a clogged strainer or pump inlet (usually hair), a stuck or reversed check valve, a wiring or fuse fault, or a worn-out pump. Work through them in that order and you will find the problem in most cases, usually without buying a new pump.

How a Boat Shower Sump System Works

On most boats the shower floor sits below the waterline, or too close to it, for water to drain overboard by gravity. Instead, the shower drains into a small sump box or tank. When the water rises, a float switch turns on a pump that empties the sump overboard (or into a grey-water tank). Typical components are:

• Sump box with one or more inlets from the shower (and sometimes sinks or the air-conditioning condensate).
• Pump, either a submersible pump inside the box or a diaphragm pump mounted outside it.
• Float switch, mechanical or electronic, that turns the pump on and off.
• Strainer or filter to catch hair before it reaches the pump.
• Check valve in the discharge line to stop water running back.
• Discharge hose, vented loop and through-hull, often with a seacock.
• Fuse or breaker and switch panel, often with a manual override.

Some boats skip the sump box and connect the shower drain straight to a diaphragm pump such as a Whale Gulper or Gusher, operated by a switch. Diaphragm pumps tolerate hair and soap better than small submersible pumps, which is why many owners switch to them.

Step-by-Step Troubleshooting

Before you start, turn off power to the pump at the breaker, and have rags, a bucket and a small flashlight handy. Shower sumps are usually smelly; vinegar and a sponge help.

1. Check power: fuse, breaker and switch

If the pump does nothing at all, start with the electrics. Check the breaker or in-line fuse, then the panel switch. If the pump has a manual override, try it. With a multimeter, check for voltage at the pump connections with the switch on. Corroded butt connectors are common in damp bilges; cut back to clean wire and use heat-shrink connectors.

If the pump runs on manual override but not automatically, the problem is almost certainly the float switch.

2. Free or replace the float switch

The float switch is the single most common failure. Soap scum and body oils coat the float until it sticks, or hair wraps around the hinge. Electronic (sensor-type) switches can be fooled by a film of residue.

• Lift the float by hand. If the pump starts, the switch works but was stuck: clean it thoroughly.
• If the pump does not start when you lift the float but does on manual override, the switch has failed. Replace it.
• If the float switch is built into the pump, consider replacing the unit with a pump plus a separate, more robust float switch. Switches fail more often than pumps, so having them separate makes future repairs cheaper.
• Make sure the float has room to move freely and is not resting against the pump body or the side of the box.

3. Clean the strainer and the pump inlet

If the pump runs but the water drains slowly or not at all, look for a clog. Hair is the usual culprit. Open the strainer (most have a screw-off bowl), clean the screen, and check that the bowl seal is intact. A cracked bowl or a poor seal lets air into the suction line, and a diaphragm pump will then run without drawing water. Bowls left full of water over a freezing winter often crack.

Next, remove the pump and clear the inlet screen and impeller housing. On diaphragm pumps, check the valves (often duckbill or flapper valves) for hair and debris; even a single strand of hair can stop a valve from seating.

4. Check the check valve

A check valve that sticks closed stops the pump from discharging; one that sticks open lets water flow back into the sump, so the pump cycles on and off repeatedly. Remove it, clean it, and make sure it is installed in the right direction. Some submersible pump makers recommend a small air-relief hole between the pump and the check valve so trapped air does not stop the pump from priming; follow your pump’s instructions.

5. Inspect the discharge line and through-hull

Make sure the seacock is open, the hose is not kinked or collapsed, and the vented loop is not blocked. Soap scum and marine growth can build up in the discharge hose and at the through-hull. A hose that has been squeezed flat behind a locker will also restrict flow.

6. Test the pump itself

If power is reaching the pump and the lines are clear but it still will not move water, bench-test it with a direct 12-volt supply. If it hums but does not turn, or turns weakly, the motor or impeller is worn and the pump should be replaced. Carrying a spare pump and float switch is cheap insurance on a cruising boat.

Symptom Guide

Symptom	Likely cause	Fix
Pump never runs	Blown fuse, tripped breaker, failed switch, bad connection	Check power, override and wiring
Runs on override only	Float switch stuck or failed	Clean or replace the float switch
Runs but no water moves	Clogged strainer, air leak at strainer bowl, stuck valve, failed impeller	Clean strainer and valves; check seals; test the pump
Drains slowly	Partial clog in strainer, pump inlet or discharge hose	Clean the whole flow path
Pump cycles on and off	Check valve leaking back; float set too sensitive	Clean or replace the check valve; adjust float
Runs constantly	Float stuck up; water leaking into the sump from another source	Free the float; trace the extra water
Bad smell	Soap scum and organic buildup in the sump	Clean and flush the sump regularly

Preventive Maintenance

A little routine attention prevents most failures:

• Use a hair catcher on the shower drain and empty it after every shower.
• Flush the sump with fresh water after showers so soapy water does not sit and cool, which is when oils solidify.
• Clean the sump and float every few months. A solution of white vinegar or a mild enzyme cleaner helps loosen scum.
• Clean the strainer monthly when the boat is in regular use.
• Use less soap and conditioner, or switch to products that rinse cleanly; conditioner residue is particularly hard on float switches.
• Winterize by draining the strainer bowl and pumping non-toxic antifreeze through the system if your boat sees freezing temperatures.

Add the shower sump to your sailboat maintenance checklist so it gets looked at regularly alongside the heads; our guide to common marine toilet problems covers many of the same hose and valve issues.

Upgrading a Troublesome System

If your sump keeps failing, consider an upgrade rather than repeated repairs:

• Separate the float switch from the pump, or use a pump with a more reliable switch.
• Fit a dedicated shower drain diaphragm pump with a strainer; these tolerate hair and soap better than small submersibles.
• Install the strainer where you can reach it easily; if it is hard to clean, it will not be cleaned.
• Choose a sump box that seals well, since cheap boxes may leak around the lid when the boat heels.
• Mount the pump close to and slightly below the sump for easier priming, in a spot where any drips go into the bilge.

Never simply remove the sump and let shower water drain into the bilge. Soapy grey water in the bilge breeds smells, fouls the bilge pump float switch and is unpleasant for anyone who buys the boat after you. Also remember that your battery charging setup has to keep up with any pumps that may run while you are away.

Shower Sump Pump Troubleshooting: Summary

• Check power first: fuse, breaker, switch and connections.
• If the pump works on override only, the float switch is the problem.
• If the pump runs but does not drain, clean the strainer, pump inlet and valves.
• Check the check valve and discharge line for blockages or backflow.
• Prevent problems with a hair catcher, regular cleaning and fresh-water flushing.