What is the water flow sensor.
The water flow sensor is just as it's name says, it is use to tell a system that water is flowing. Seen to the right is the water flow sensor used in many of the Bestway, Coleman and Lay-Z-Spa branded inflatable hot tub models. These sensors are one way flow sensors meaning that they will only sense water flowing in one direction. Failure of this sensor is one of the causes of the dreaded E01 or E02 errors seen on the pump/heater unit of many of the listed brands of inflatable hot tubs.
How does the flow sensor work?
The operation of the water flow sensor is very simple. There are three main components to the sensor. The first part is the main sensor housing. The housing has water inlet and outlet ports for the water to flow through. The second part is the magnetic reed switch, or proximity switch. This part is the small black tubular piece with the two wires coming off of it like the one seen to the right. When this piece senses a magnetic field, a small switch inside makes contact completing the circuit in the two wires. The third part of the sensor, quite obviously, is the magnet. The magnet is housed in a small plastic paddle like the one seen to the left. When water is pushed through the sensor housing, this magnetic paddle will get pushed up near the proximity switch triggering it telling the system that water is in fact moving. This sensor is a one way sensor meaning that it will only sense the flow of water in one direction. Because of this, care must be taken to install this sensor in the correct direction for proper operation.
The main problem with these sensors.
The biggest problem with these sensors is that the magnetic paddles in them fail. The reason for this is because magnets can easily start to rust if exposed to water. Why do magnets rust? Magnets work because they are made of ferrous metals which contain iron. Magnets need iron to attract, and iron rusts when exposed to oxygen and water. Rust reduces the attraction of a magnet. This is why the sensors fail when the magnet gets rusty. The original sensor paddles have the magnet inset into a hole in the center and then a dab of epoxy glue is put on top. Over time, the dab of epoxy can come loose from the paddle exposing the magnet to the water eventually causing it to rust and fail. The plastic around the magnet will start to crack because of the magnet swelling which allows more water in causing it to snowball into failure.
Inspecting your sensor.
How do you find out if your sensor has failed or is starting to fail. The first thing is to unplug your pump from the mains socket. Never work on your unit with the power plugged in. Now place your black rubber water stopper caps, seen on the left, over the water ports inside your tub. This is to prevent water flowing out of the flow sensor when you take the cap off. Next, remove the cover from your pump/heater unit by removing the six screws in the middle of the unit as indicated in the picture to the right. Once those screws are removed, carefully lift the top off being careful of the ribbon cable. Now, separate the black connectors on the ribbon cable slightly down from the control panel inside and set the cover to the side. In the picture to the left, the arrow points to the water flow sensor. Start by disconnecting the small plug on the two wires attached to the top of the sensor. Now remove the four screws from the top of the sensor and set them aside. Carefully lift the top of the sensor off being careful not to loose the round o-ring seal under the cap. Inspect the plastic paddle under the cap looking for signs of cracks in the plastic, and signs of rust like the one shown to the right. If you see any of these things or other damage to the paddle, it is best to replace it. While you have the top off, you should also inspect the o-ring for any signs of wear. If there is even the slightest bit of wear on the o-ring, it is best to just replace it. Some would have you replace the entire water flow sensor assembly which can cost you between $50 and $75 US dollars just for the part. On top of that you would have to dismantle the unit even further to be able to remove the old one and install the new one. Why replace the whole sensor when you can just repair it.
Testing the sensor
To test the water flow sensor you will need a multimeter set to the continuity setting that will indicate an open or short condition. If your multimeter does not have a continuity setting you can put it on a resistance setting to show either infinite resistance or zero ohms (or near zero). You will also need two small pieces of stiff wire like in the picture to the right. The wires will be used to connect to the sensor to do the tests. Start by wrapping the small wires around the tip of the test probes and inserting them in the two holes in the connector. You will feel a bit of resistance when pushing the wires in, but they should be inserted enough to make a good connection with the connectors inside. Once connected, the water flow sensor should show an open or infinite resistance when the paddle is hanging down and a short or zero ohms when the paddle is in the upward position resting on the cover plate. If you don't read a shorted condition when the paddle is in the up position, you most likely have a problem with the paddle magnet. The sensor that senses the magnetic paddle is the black tube looking part that the wires connect to. It is extremely rare that that part will fail. If you have another small neodimium rare earth magnet (refrigerator magnets may not be strong enough) you can place it near where the paddle will hit the cover and see if the sensor triggers. If it does, then your paddle needs to be replaced. I sell both the replacement paddles as well as kits that include the paddle and the o-ring seal for the top of the sensor housing. Both the paddle and the kit version come with a replacement nylon pin to attach the paddle as many times these get broken. You can get both at my web store by clicking here. On the extremely rare chance that the sensor ( black tube) is bad, you may need to contact Bestway or purcase a new water flow sensor, but as mentioned, it is extremely rare that this part goes bad.
Repairing the sensor.
To repair the flow sensor you should by now know what parts you will need for the repair from the inspection you just did above. Whether you nee just the paddle, or the paddle and o-ring, we have you covered. If all you need is the water flow sensor paddle, this can be purchased from our store as a kit that now includes the retaining pin for $10.49 plus shipping by clicking here. If you also need the o-ring, we sell a kt that contains the paddle, retaining pin and the o-ring. These kits can be purchased from our store for $11.49 plus shipping by clicking here. If you decide that you want to go to someon else to purchase the paddle, there are some things that you need to watch out for. Be weary of the ones like the one on the right. In this style, the magnet is mounted directly on the top, completely exposed to the water. Because of this, the magnet will start to rust and fail significantly quicker than the ones that I sell in which the magnet is completely sealed in plasic. The other thing with paddles like this one is that people make these out of PLA plastic. This type of plastic has a lower melting point and if exposed to too much heat, it will start to deform. Once the plastic deforms, the magnet can pop out of it's hole causing another failure. Our paddles, seen on the left, are made completely from ABS plastic which is more flexible and has a lot higher melting point making it less prone to deforming and failure. Also the magnets on our sensors are completely encapsulated in plastic with little to no chance of the magnet touching water and rusting. Buy our parts with confidence.
Now on to replacing the sensor paddle. These sensors use a small nylon retaining pin to secure the paddle to the sensor cap. This can easily be removed by pushing on the back side of the pin, the side with the slot in it, with something flat. The pin should come out pretty easy. Simply pull the pin out enough to allow you to get the old paddle off. Put the new paddle in place and push the pin back through the hole. Our kits now include the retaining pin. It's that simple. Once you have that done, if needed, remove the old o-ring and drop the new one in it's place. Be sure to inspect and clean the channel that the o-ring sits in prior to installing the new one.
So that's it, you just repaired your water flow sensor for under $16 US dollars rather than spending $50 plus and all the extra time and effort