Salt Cell Low Output vs No Output Decision Tree

Why this matters

A salt chlorinator is the single most expensive consumable on a salt pool, and customers conflate "no chlorine in the water" with "the cell is bad." A cell that tests as healthy can read as failed because the controller has the wrong salt input, the flow switch is gunked, or the water is stabilizer-blocked. A tech who replaces every low-output cell at face value buys cells the pool did not need; a tech who refuses to replace a genuinely worn cell sends the customer back to bagged chlorine and loses the next opening. The tree below separates a real cell failure from the five things that masquerade as one, ordered by what comes through the truck radio most often.

Symptom presentation

Pattern A: cell reports normal current, chlorine residual is zero or trace. Pattern B: cell reports low or no current with the controller showing a fault code. Pattern C: cell makes chlorine at boost or super-chlorinate but nothing at the normal output percentage. Pattern D: cell output drops noticeably year over year - what used to hold 3 ppm at 60 percent now needs 90 percent. Pattern E: cell shows scale visible through the housing.

Quick checks - 8 minute pass

1. Salt level (tested with a refractometer or drop kit, not the controller's reading). Most cells need 2700-3400 ppm. Below 2400 the cell will undervolt and either de-rate or fault.
2. Stabilizer (cyanuric acid). Above 100 ppm chlorine is locked, residual will read low even with the cell producing. Above 50 ppm efficiency drops 5-10 percent per 10 ppm.
3. Free chlorine residual measured at the return jet with the cell running. Zero residual with cell running and visible bubbles equals demand load - shock or algae bloom, not a cell problem.
4. Water temp. Below 60 F most cells throttle 50 percent or shut off; below 50 F they shut down entirely. Customer running pool in spring at 55 F has a working cell that is not allowed to produce.
5. pH. Above 8.2 the chlorine that is produced is mostly in the hypochlorite-ion form and reads ineffective; correct pH before judging output.

If quick checks return all-normal, proceed to isolation.

Isolation tree

Step 1 - Bubble check

Open the union, observe the cell with the pump running and the chlorinator commanded ON at 100 percent. Bubble stream from the plates equals current is flowing. No bubbles equals no current. This is a 10-second test that splits the entire problem into electrical (no bubbles) vs water-chemistry/cell-wear (bubbles present).

Step 2 - Bubbles present, residual is low

Cell is producing. Problem is downstream consumption or measurement.

• Confirm stabilizer 30-50 ppm range. Above 80, partial drain and refill.
• Confirm the cell is producing for enough runtime. A 25K gallon pool with a 40K rated cell at 50 percent output running 8 hours summer is borderline; bump runtime before bumping output.
• Confirm phosphate level. Above 500 ppb phosphates feed algae that consume chlorine faster than the cell can produce. Algaecide and phosphate remover, not a new cell.
• Confirm no algae bloom in progress. A pool turning corner-green is consuming 1-2 ppm per hour - shock first, then judge.
• Confirm the heater bypass is not routing flow around the cell.

Step 3 - No bubbles, controller faults

Controller fault code drives the path:

• Low Salt or Inspect Cell - cell is dirty, scaled, or worn. Pull and inspect. Hydrochloric acid clean if scale visible (1:4 acid to water in plastic bath, plates only, do not submerge connector). Brush with plastic brush only, never metal.
• No Flow - flow switch dirty, paddle stuck, or pump speed too low. VSP at 1500 RPM may not push the flow switch closed. Bump speed to 2400 RPM and retest. Clean paddle with vinegar.
• High Salt - controller misreads conductivity when water temp is low or salt is layered after a fresh dose. Mix the water 24 hours, retest.
• Service Cell or Replace Cell - end of useful life, voltage cannot drive current at any salt level. Confirm with a known-good cell swap if available, otherwise replace.

Step 4 - No bubbles, no controller fault

Path of probability:

• Cell cable disconnected at the controller or corroded at the cell end. Pull, clean, dielectric grease, reconnect.
• Boost or super-chlorinate timeout has parked the cell at zero. Cycle the controller.
• Flow switch wire chafed or pinched - shows always-no-flow even when paddle is open. Continuity test.
• Time-clock in OFF window. The controller will not chlorinate during pump-off scheduled hours. Verify schedule against actual demand.
• Cell at end of life with no controller alarm (older controllers do not throw a code, they just stop bubbling). Voltage test at the cell terminals during a commanded ON cycle - if voltage is present and current draw is zero, cell is dead.

Step 5 - Pattern D, slow drift

Cells are consumable. Field-typical life:

• Hayward T-15 - 3-5 years at 8 hr per day, 25K gal.
• Pentair IC40 - 3-7 years at typical residential duty.
• Jandy AquaPure - 4-6 years.

A cell at 50 percent of new output is at end of useful service. Replace, do not nurse.

Confirming the diagnosis

Refractometer salt reading at the cell, not the controller. Clamp meter on cell cable during commanded ON to read amps. Voltage probe at cell terminals. Visual inspection: white scale, calcium bloom, or worn pitted plates with copper showing on bond points equals failed cell.

Remediation

• Scale only: acid clean, return to service.
• Worn plates: replace cell. Match to flow rate and pool volume.
• Flow switch: clean or replace. Do not bypass.
• Controller board: fault codes that persist across known-good cell swap point to controller. Replace board, not cell.

References

• ANSI/APSP/ICC-11 Water Quality in Public Pools and Spas, free chlorine reference.
• Hayward T-Cell Series Owner Manual, troubleshooting section.
• Pentair IntelliChlor IC40 Installation and User Guide, fault codes.
• Jandy AquaPure 1400 Installation Manual, electrolytic cell service.
• CDC Healthy Swimming Program, chlorine effectiveness vs cyanuric acid.