Troubleshooting a Faulty Submersible Bilge Pump

Not long ago we wrote about how to install a submersible bilge pump, that thankless piece of gear primarily designed to keep nuisance water from collecting in your bilge. But the fact that such a pump can also buy time in case your boat is flooding also makes it an important piece of safety equipment.  Unfortunately these pumps live an unglamorous life, often in smelly, dirty, slimy conditions. It’s those conditions that give bilge pumps a fairly high potential to fail.

Bilge pumps live in deep nooks that naturally collect dirt, hair, and general grunge.  They have to be robust, and they have to be maintained. All photos: Doug Logan

Bilge pumps live in deep nooks that naturally collect dirt, hair, and general grunge. They have to be robust, and they have to be maintained. All photos: Doug Logan

Since there are all sorts of components in your submersible bilge pump setup that can go bad, it’s good to know which steps to take first before giving up, tossing the pump out, and installing a new one—especially if your pump isn’t even bad. Following the steps we’ve outlined here should get you back up and pumping again soon.

Pump Runs But Doesn’t Pump Water

First, see if you’ve got a clog or a pump failure. If the pump is running but no bilge water is being discharged, carefully remove it from its mounting base and check for debris both in the pump intake and in the base itself. Also look for bits of debris that may have jammed the small plastic impeller inside the pump, which is often visible. Clean out any offending debris and see if that fixes the problem. Also check the impeller itself to make sure it hasn’t shattered or come loose from its drive axle.

If there are no apparent clogs in the pump base or intake, remove the discharge hose, clean off the end, and blow on it to see if there’s an obstruction. Alternatively you can bring a garden hose down in the bilge and try running pressurized water through the discharge hose to clear any blockages. If you do this and water comes out the discharge, you know it’s free of blockages. Reconnect the pump and try again.

Check the strainer and discharge hose for clogs. Also check the pump impeller. This one has broken loose inside its housing.

Check the strainer and discharge hose for clogs. Also check the pump impeller. This one has broken loose inside its housing.

If it still doesn’t pump water out of the discharge thru-hull,  check along the full length of the discharge hose to make sure there are no failures in the hose itself and that all the hose clamp connections are solid. If you have a vented loop installed in the discharge line, remove the vent cap on its top to make sure the duckbill valve inside isn’t obstructed. Also investigate any inline check valves your system may have for blockages or failure.

Still no joy? The likelihood is that the bilge pump is faulty and should be replaced.

Pump Does Not Run at All

The next most common scenario is that the bilge pump won’t run at all, and this means you’ll need to do some electrical troubleshooting. Fear not, though. Even electrical newbies can easily troubleshoot a submersible bilge pump that’s on the fritz.

This may sound silly, but the very first thing you should do is ensure that the bilge pump’s control switch or circuit breaker toggle is switched to the “on” position. Also make sure your battery or batteries aren’t dead. You can do this by checking the voltmeter on your electrical panel; looking to see if other electrical gear on the boat is working; or by testing your battery or batteries with a multimeter. If you have a battery selector switch, make sure it’s switched to the correct battery bank.

To check wiring and electrical current you'll need to invest in a decent multimeter. Basic ones are inexpensive and a good investment.

To check wiring and electrical current you’ll need to invest in a decent multimeter. Basic ones are inexpensive and a good investment.

Next, if you’ve got a control switch with an integrated fuse in it, check to see if the fuse is blown. If it is, replace it and see if the bilge pump switches on. Control and circuit breaker switches can also go bad. This is much less likely, but check to ensure the wire terminations at your control switch or breaker are connected and not loose.

Considering you’ve got juice in your batteries and your circuit protection and switching devices are connected and working properly, you’ll next need to go down to the bilge and check on the electrical connections for the bilge pump itself. Once you’ve turned yourself into a pretzel inside your bilge, check all the electrical splices and connections leading to your pump to make sure that they’re securely connected. If everything appears OK, you will need to use a multimeter to see if electrical power is making it all the way down to the bilge, starting with the primary positive and negative leads that power your bilge pump, well before any float switches, which we will discuss shortly. (If you don’t have a multimeter, you really should run out and get one—it’s an essential tool to have in your boat’s tool bag.)

Making sure you’ve turned off electrical power to the pump leads, cut both the positive (red) and negative (black) wires ahead of any float switches that may be wired to your pump. Next, with the wires separated and the insulation removed from a small section of each end to expose the wire strands inside, turn power back on to the bilge pump and then touch the positive and negative multimeter probes to the appropriate wires to see if there is any current. With the multimeter switch selected to read volts, you should see anywhere between 12.4 to 14 or so volts on the display (assuming you have a 12-volt system like most boaters). If you see nothing—assuming you’ve checked your fuses, switches, circuit breakers, and their electrical connections—there’s almost certainly a fault in the wire somewhere and it should be replaced.

If you’ve got power at the bilge pump supply wire’s lead, it’s pretty likely that you’ve got a float switch failure. With that said, know that some submersible bilge pumps have their own “brain” and internal float switch that signal the pump to turn on and off. If your bilge pump is one of these and is directly wired to the power supply, yet it’s still not working (despite having good electrical juice flowing from the supply wire and you’ve checked for clogs) it’s likely the internal float, brain, or motor have gone bad. In this case it’s probably time to shop for a new pump.

Butt connections in heat-shrink terminals can last a long time in a wet environment, but not forever before corrosion seeps in.

Butt connections in heat-shrink terminals can last a long time in a wet environment, but not forever before corrosion seeps in.

Bilge pumps are more commonly fitted with external float switches, however. The float switch is normally installed near the submersible bilge pump itself and often looks like a white plastic block on a hinge, though it can be other shapes and colors. A float switch works by floating upwards as water fills the bilge. When it floats high enough, an electrical connection is made, turning the pump on.

Float switches are usually mounted inline with the positive (red) wire leading down to the bilge pump, though some have an auto-on-off switch installed inline. To check if your float switch is working or not, cut the wire leading from the float switch to the pump, stripping back a bit of insulation to expose the wire strands inside. Next take the negative power supply lead supplying the bilge pump, and also cut back some insulation to expose the wire strands inside, if you haven’t already. Connect the probes from your multimeter to the positive wire from the float switch and the negative lead from the boat’s electrical system, and then lift the float by hand. If you read any voltage over about 12.3 volts, your float switch is OK and your pump is likely faulty. If you read no voltage with the float lifted, the float switch is almost surely bad, meaning you need to replace it.

Phew! Though all of this may sound as if you’ll have a solid weekend lined up in getting your bilge pump back up and running, it realistically should only take an hour or two. Before you know it you’ll hear the sweet flow of water pouring overboard form your bilge.

 

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