Hayward Sense & Dispense No Display / No Power: Step-by-Step Diagnosis
Quick Summary
- The CSM module in the flow cell receives power through the COMM cable from the main control board. A blank or dead display on the module means no power is arriving via that cable.
- Work in order: verify the main board has power → check the COMM cable for damage → confirm the cable connector is fully seated → measure 10–15VDC at COMM pins 2 and 4.
- If voltage is absent at the COMM port, the main board (GLX-PCB-PRO or GLX-PCB-AR-PRO) is the likely fault — not the CSM module.
- If voltage is present but the module is still dead, replace the module: GLX-SD-ELEC-MOD.
- The CSM module does not have a fuse. If the main board is confirmed healthy, replace the module.
How the CSM Module Gets Power
The Chemistry Sensing Module (CSM) is the electronic assembly inside the flow cell housing. Unlike the control panel, it does not plug into wall power directly. It receives both its communication signal and its operating voltage through a single COMM cable that runs from the flow cell back to the main ProLogic or AquaRite Pro control board. The cable delivers 10–15VDC on pins 2 (Black) and 4 (Red).
This means a dead CSM display can be caused by the control board, the cable, or the module itself — you need to trace power from the board to the module to determine which component failed.
Panel Safety
Opening the ProLogic or AquaRite Pro control panel enclosure exposes high-voltage terminals. Turn off the main breaker serving the control panel before opening any covers. Only qualified technicians should access internal panel wiring. The COMM port voltage test (10–15VDC) requires the panel to be powered on — exercise caution and use a properly insulated multimeter.
Step-by-Step Diagnosis
Step 1: Verify the Control Panel Has Power
Before opening anything, confirm the ProLogic or AquaRite Pro display is functioning normally. If the main control panel is also dark or not responding, the problem is upstream of the Sense & Dispense system — check the main breaker feeding the equipment panel, then the sub-breaker or GFCI protecting the control panel circuit.
If the main control panel display is working but the CSM module in the flow cell is dark, proceed to Step 2.
Step 2: Inspect the COMM Cable
With the system powered off, do a complete visual inspection of the COMM cable from the flow cell housing back to the control panel. The COMM cable is a multi-conductor low-voltage cable — typically smaller diameter than the power wiring. Look for:
- Physical cuts or breaks in the cable jacket
- Pinch points where the cable passes through conduit, under equipment, or through wall penetrations
- Evidence of rodent chewing, particularly near the ground or inside enclosed equipment pads
- Corrosion or water damage at either connector end
If the cable is damaged, it must be replaced as a complete assembly. Do not splice. A damaged COMM cable that still delivers partial voltage will cause intermittent behavior — the module may power on sometimes and not others. If the cable appears intact, continue to Step 3.
Step 3: Confirm the COMM Connector is Fully Seated
With the power off, disconnect and re-seat the COMM cable connector at the main board's COMM port. Push the connector firmly until it clicks or seats completely. A partially inserted connector can fail to make electrical contact with some pins while appearing visually plugged in.
Also check the connection at the flow cell end if accessible. Re-seat that connector as well. Restore power and check whether the CSM module displays anything. If it remains dark, proceed to Step 4.
Step 4: Measure Voltage at COMM Pins 2 and 4
With the system powered on and the COMM cable disconnected from the board's COMM port, use a digital multimeter set to DC voltage to measure across pin 2 (Black wire) and pin 4 (Red wire) of the COMM port on the main board. The expected reading is 10–15VDC.
- If 10–15VDC is present: The board is providing power correctly. The fault is either in the COMM cable or the CSM module itself. If the cable passed visual inspection, replace the CSM module: GLX-SD-ELEC-MOD.
- If voltage is absent or below 5VDC: The main board is not supplying power to the COMM port. If another COMM port is available on the board, test that one as well. If no COMM port produces voltage, the main board needs to be replaced: GLX-PCB-PRO for ProLogic, GLX-PCB-AR-PRO for AquaRite Pro.
After Restoring Power
Once the CSM module powers on and the display comes back, allow the system to run for at least 30 minutes before checking the probe readings. The probes need time to stabilize after being without power or flow.
After the readings stabilize, test both the flow cell water and pool water independently with a calibrated test kit. If the pH probe reading differs from your independent test by more than 10%, run the pH Calibration Wizard before leaving. The ORP probe does not need calibration — only cleaning if the readings are unreasonable for the current chlorine level.
If the CSM was dead for an extended period, manually test and treat the pool water. The system was not dosing during the outage, and the pool chemistry may have drifted significantly from target values.
Frequently Asked Questions
The CSM module display comes on briefly and then goes dark. What does that mean?
Intermittent power that comes on briefly and dies usually indicates a connector or cable problem. The module is getting enough voltage to start up but not to sustain operation — typical of a partially seated connector, a corroded pin in the connector, or a cable with an internal break that makes contact only under certain conditions (temperature, cable position). Disconnect and thoroughly clean the COMM connector pins, re-seat, and observe. If the behavior persists, replace the COMM cable.
Is there a fuse in the CSM module?
No. The GLX-SD-ELEC-MOD does not have a user-serviceable fuse. The overcurrent protection for the COMM circuit is located on the main control board. If the CSM module has failed due to an overcurrent event, replacing the module is the correct repair.
The main board was replaced but the CSM still shows no power. Why?
After replacing the main board, verify that the COMM cable is connected to the new board and that the new board is fully initialized and running. Some replacement boards require the system to boot and configure before the COMM ports are energized. Wait two to three minutes after boot before measuring COMM voltage. If voltage is still absent after full boot, check whether the new board was configured correctly — a ProLogic board with incorrect firmware or programming may not energize all output ports.
Can I test the CSM module's health independently?
Not easily in the field. The GLX-SD-ELEC-MOD requires the COMM cable voltage to power on and respond. You can confirm it is receiving adequate voltage (10–15VDC at pins 2 and 4) and if it still shows no display or no response, the module is failed. There is no standalone bench test procedure for the CSM module — the diagnosis relies on process of elimination: confirm board voltage is correct, confirm cable is intact, then replace the module.
What happens to dosing while the CSM is without power?
When the CSM module is not communicating — whether due to no power, a comm error, or a damaged cable — the system cannot read pH or ORP. Both dosing circuits (acid and chlorine control) are suspended. The pool will drift during any CSM outage. On pools with high demand (hot weather, heavy bather load), this can mean significant chemistry drift within 24–48 hours. Always test and manually treat the water when correcting a no-power situation.