This is a water flow issue, the flow sensor is not satisfied there is adequate water flow. Most of the time it is an external pump flow failure, often related to an air trap. Once it was a flow switch that was sticky, it acted intermittent, in Nanaimo, and was replaced It showed rub marks on the corners from the pipe. The majority of fixes are external to SunPump, it is rare for the flow switch to fail, It can be misaligned for direction or rub against the pipe. 


The tall, fridge-sized SP2.3 and later SP3.1 do not have a flow switch, the exchange is internal by the compressor with need for a pump.


The Flow Sensor is like a simple paddle switch. When the pump moves then water flow pressure moves the paddle and closes a circuit allowing power to flow and the compressor to come on. The compressor will not start if the circuit is open for any reason. The paddle can be trimmed if it is too long, clipping a tiny amount off the corners so it does not rub against the pipe interior. Look for signs of rubbing at the corners,, and trim only a tiny amount with snips.


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A temporary work-around is to use a Red to White wire jumper to keep the circuit closed, until the part can be replaced. 
The wire is part of the sensor - do not try to remove the wire from the encased sensor body. The wire can be traced to a connector in the Electrical Compartment of the SunPump, in most models it is near the upper left corner. .

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The fine striped wires above are for the sensor. Verify by tugging on the black cord from inside the cabinet connected to the flow sensor.

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The Flow Sensor has a direction to work properly. It points out of the SunPump top 1-inch water line.



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The flow sensor is easily accessible by removing the top panel. The location is shown above in the red circle with the sensor removed, you are seeing the 3/4-inch brass BSP (European) threads on a Tee near the front and top pf the cabinet, just 6-inches inside from the 1-inch hot water outlet pipe.



Error Reason | Solution  water flow Error 

 1, water flow switch installation irregularities or direction is not correct 1, find out the reason, adjust the direction, correct installation flow switch

 2, water pipeline system with air 2, open the discharge valve or water valve, eliminate the air in the piping

 3, water system or filter is block 3, clean the filter, clean the pipe

 4, water system lack of water 4, hydrating and eliminate the air in the piping

 5, water flow switch is broken 5, change a good water flow switch

 6, water flow switch wiring is wrong 6, find out the reason, correct water flow switch wiring

 7, water flow switch blade is too long and block in the pipeline 7, find out the reason, adjust the blade's lenguth , correct install the flow switch

 8, water pump broken 8, replace the pump

 9, water pump choose is too small 9, replace a water pump which meet the requirements of water flow volume and head of delivery

 10, water pump does not work 10, find out the reasons, troubleshooting