Pool heat pump water flow control sensor was replaced, agua link system stopped working, now repairman has advised that we need a new circuit board in heat pump in order for aqualink to work....All was working prior to sensor replacement. Please advise....

Does your pool gave an attached spa?

IF it does have a spa, dies it also have a spa side remote?
If so the first step would be to unplug the spa side remote from the back of the board.
If the issue stops then you need a new spa side remote if it persists then it nah be be main circuit board or relay for the heat pump.

I believe with some of manufacturers spas, Vita included, the error will occur if the system is reading that the pressure switch has a "CLOSED" circuit. Bypassing the pressure switch, will still be creating this! What this means to the system: The circuit board does a quick system check. If the board says to itself: "Why does the pressure switch tell me the water is flowing (thats what happens when the pump is on and moves water; pressure is created in the plumbing and the switch then closes) when I haven't even sent power to the pump yet?" Then it will send the error message.

Your switch may need to be calibrated to only close when there is water flowing, and then open within a second of the pump or water flow stopping.

First make sure that the Pump runs, if water does not flow thru the heater assembly, the heater will not turn on..., else the water would super-heat. If water is flowing thru the heater assembly, check your output from your thermostat if it is working. If not replace thermostat. If it is ok, then check to see if Pressure switch is working by using a meter and see that it is open circuit when the spa is off and a closed circuit when the pumping water. If not, then you may be able to adjust your pressure switch if it has that capability. If not, replace pressure switch. If however, the pressure switch is ok, then you should test the voltage at the heaters element. If there is voltage, then you need a new heater element. If not, then I need a more detailed description of the problem.

Hope this helps,
Dan Osko
Osko Pool n Spa
http://www.oskopoolnspa.com

make sure the heating element isnt touching the casing inside the heating tube. if its an indoor tub, make sure the filtration cycles are not set to constant. constant filter cycles on an indoor tub will generate residual heat from the circ pump running 24/7, causing tub to heat past 104 degrees

Use a high quality external temp probe and make sure the temp sensor in your system is correctly reading the water temp.
If the water is truly 110 then you may need to replace the board completely.

go to system setup see aquapure turn chlorine production 5% or more and you should see it on the menu

After five years of using our pool each summer, we assembled it last week and I kept getting the "low flow" warning (with irritating beeping) even though the water flow was very good. I disassembled the unit and checked the flow switch, and found that the switch itself was the culprit. Here's what I did: (this is probably not recommended by Intex...) I unscrewed the main portion of the salt water purifier (the part with the digital display on top) from the base and lifted it up to expose the circuit board and wiring. All the fuses were intact and everything looked good. At the bottom of the circuit board, about an inch from the right edge is where I found the connections for the flow sensor. One was marked "flow" and the other was "grnd". I removed the plugs that run to the slow switch, closed the circuit by making a direct connection between the two plugs, and voila! No problem. I ended up cutting the wires about 1-1/2 inch from the plugs and connecting them with a wire nut, then I plugged them back in. The unit is working perfectly again.

If you attempt this, make sure the unit is unplugged and be careful when dealing with the circuit board. Don't be intimidated, it's not a high-voltage connection you are working with, you are simply closing the circuit and telling the board that the switch is closed as it would be with adequate water flow. I was comfortable making this "modification" and bypassing the flow sensor because we have several years of experience with our pool and because I clean and swap out our pump filter every day during summer, and because we know the difference between strong and weak flow just by checking the inlet and outlet ports in the pool.

I hope this helps someone! It took care of my problem. Best of luck.

What kind of pump are you using?
Sounds like the Intex is restricting water flow there by heating up your pump and shutting it down..
You may need to re plumb everything to handle the flow.
Intex hoses and fittings are different than the industry standards just so the can make you buy from them
Do what ever it takes to get good flow