IntelliChlor Showing a Flow Error With the Pump Running? How to Test the 520736 Flow Switch
There's a specific kind of frustrating: standing at the equipment pad watching water move through clear pipe while your salt system insists nothing is flowing. The cell isn't making chlorine, the free chlorine in the pool is sliding toward zero, and nothing looks wrong.
On a Pentair IntelliChlor, that situation almost always points at one part. The flow switch. And Pentair sells it as the 520736 flow switch replacement kit so you don't have to buy a whole new cell.
What does the flow switch on an IntelliChlor do?
It's a safety device. The flow switch tells the system that water is actually moving through the cell, and the system refuses to generate chlorine unless that signal is present.
That rule exists for a good reason. A salt cell producing chlorine in standing water builds up hydrogen gas, and that's a real hazard, not a warning label formality. So when the switch stops reporting flow, the IntelliChlor shuts chlorine production down and waits. It's doing its job even when the switch itself is the thing that's broken.
Why does my IntelliChlor say no flow when the pump is running?
If the pump is running at a decent speed and the flow light still won't come on, the switch is either dirty, stuck, or dead. Those are the three outcomes, in that order of likelihood.
Here's what typically causes it:
- Scale and calcium buildup coating the switch so it can't move or sense properly.
- Debris packed around the switch, usually after a filter cleaning or a bad basket.
- A cracked or corroded switch body that lets water in where it shouldn't be.
- A damaged wire or corroded connector between the switch and the cell.
- Actual low flow from a clogged basket, dirty filter, or a variable speed pump set too low.
That last one catches a lot of people. If you recently dropped your pump speed to save power, you may simply be below what the cell needs to register flow. Bump the speed up during the chlorination schedule and see if the error clears before you buy anything.
How do I test the 520736 flow switch?
The quickest test is a continuity check with a multimeter. A working flow switch is open with the pump off and closed with the pump running.
Do it in this order:
- Shut the pump off at the breaker and let pressure bleed off at the filter.
- Disconnect the flow switch leads and set your meter to continuity.
- With no flow, you should read open. If it reads closed with the pump off, the switch is stuck and needs replacing.
- Reconnect, restore power, and run the pump. The switch should now close and the flow indicator on the IntelliChlor should light.
- If it stays open with good flow, the switch has failed.
One warning worth taking seriously: do not leave a jumper across the flow switch terminals to make the error go away. People do this and it defeats the safety that keeps hydrogen from collecting. Use a jumper only for a few seconds as a diagnostic, then take it out.
How to replace the flow switch
Cut power to the pump and the IntelliChlor power center at the breaker before anything else. Close the isolation valves and relieve pressure at the filter.
Then pull the old switch, clean out any scale in the port, install the new switch from the 520736 kit with the supplied seal, and route the wiring back the way it came. Snug the fitting by hand and give it a light turn with a wrench. Overtightening plastic here is how a small job turns into a bigger one.
Open the valves, restore power, and watch for the flow indicator to light within a minute of the pump running.
What if the flow switch isn't the problem?
If a new switch doesn't clear the error, look upstream. Check the basket, the filter pressure, and the pump speed first, since those are free to check.
After that, the fault is usually in the cell's own electronics or in the power center. Those are separate parts with separate symptoms, and swapping the flow switch first is the cheap way to rule out the most common cause before spending real money.
Is the 520736 kit worth buying?
Compared to a complete IntelliChlor cell, yes, easily. A flow switch is a fraction of the cost of a cell, and if the cell itself still has life left in it, replacing one small switch gets your salt system back online for a fraction of the price.
Where it stops making sense is when the cell is already near the end of its service life and the plates are worn. At that point you're putting a new switch on something you'll be replacing next season anyway.
Not sure this is the right part for your problem? Reach out and we will help you figure out exactly what you need before you spend money on the wrong thing.