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Fresh Water Pump Diagnosis

Written By Todd S. Go2marine/LFS Tech Support


Let’s go over some trouble shooting steps for testing and adjusting the freshwater pump. Issues with pumps consist of pulsing, not shutting off, not coming on, and pressure issues. The most common issue with freshwater pumps is the pressure switch failing that is on the front of the water pump.


Starting with the most common issue with these pumps, the issue of not shutting off, constantly running, or not running at all. This is normally caused by the failing of the pressure switch that is mounted on the front of the water pump. There are a few procedures to try to test this part of the pump. For the first test of the pump not running at all, verify that you have 12VDC going to the pump. If so, disconnect the power temporarily, next remove the square cover on the front of the water pump. Remove the two red wires on the front of the pump and wire them together. Apply 12VDC to the pump again, if the pump comes on and runs then the pressure switch is bad. You can remove the pump from the water system for these tests it can run a few seconds without water, and it will not damage the pump. If the pump does not come on and run, then it is likely the motor is bad also.


To replace the pressure switch first remove the front cover of the pump. Next you will cut the ends off both red wires. Then use a butt connector, some pressure switches come supplied with these connectors. Use the connectors to connect the wires of the new pressure switch into the pump motor. Be sure to either take a photo or somehow label the position of the wires that come off the old pressure switch and place them in the same location on the new switch when rewiring. Next you will install the new O-ring/diaphragm and then install the switch.


If the pump is pulsing or cycling, then you most likely have a leak in the freshwater system. It is necessary to look over the freshwater system at all the connection points and lines. If after a thorough inspection of the system, there are no leaks found then the pump may be the issue. There is a small set screw in the front center of the pressure switch that is accessible without removing the cover. This is where you adjust the cut off pressure of the pump. All freshwater pumps are variable pressures, this is adjusted by turning this screw clockwise and counter clockwise to increase or decrease the pressure.