Jandy heaters are unusually good at telling you what is wrong. Between the messages on the control panel and the diagnostic light on the ignition control board, a JXi will narrow a fault to a system in seconds. What it will not do is tell you which part of that system failed, or why — and that gap is where most of the wasted money in heater repair lives.
These are the words the JXi and JXiQ put on the display. An LXi says some of them differently, noted where it does.
| Message | What it means | Usual cause | Yours to fix? |
|---|---|---|---|
| CHECK FLOW | Water pressure switch saw too little flow to fire. An LXi reads NO FLOW. | Dirty filter, pump speed too low, a valve part-closed. | Often yes |
| FAULT — HIGH LIMIT | Water in the heater exceeded the internal safety limit. | Low flow, blocked vent, or a failing limit switch. | Find the cause |
| IGNITION STEPS | Working through its ignition sequence, or stuck part way through it. | Gas supply, ignitor, or the flame sensing circuit. | Check gas only |
| SHORTED H2O SENSOR | The water temperature sensor circuit is reading shorted. | Failed sensor, damaged wiring. Rodents do this. | Technician |
| OPEN WATER SENSOR | The water temperature sensor circuit is reading open. | Broken sensor wire, disconnected sensor. | Technician |
| FUSELINK / FIELD CHECK | A fault in the heater’s safety wiring circuit. | Not something with a homeowner version. Needs tracing. | Technician |
Wording varies between JXi, JXiQ and LXi and between control board revisions, so check your model against the Jandy manual before acting. If your message is not here, photograph the display and send it over.
Open the cabinet and there is a single LED on the ignition control board that flashes in patterns. This is the part most homeowners never look at, and it is often more specific than the display.
| Pattern | What it means | What it points at |
|---|---|---|
| 1 flash | Air flow fault. | The air pressure switch is not closing, or the fan is not running properly. Blocked vent, tired blower, or something nesting in the way. |
| 2 flashes | Flame detected when the heater should not be firing. | A gas valve not fully closing, or a sensing fault. Shut the gas off at the heater. |
| 3 flashes | Ignition lockout after three failed attempts. | Gas off or low, air in the line, failed ignitor. Soft lockout, so it clears itself after about an hour. |
| On solid | Fault in the ignition control itself. | The board or its wiring. Not a reset-and-hope situation. |
Every other code on this page is a troubleshooting exercise. A two-flash pattern — flame detected when the heater is not supposed to be firing — is not. Shut the gas off at the heater, leave it off, and call us on (909) 577-5274. The same goes for a burner you can see lit when the heater should be idle.
This is by far the most common Jandy message, and the heater is almost certainly fine. It checked for water movement, did not find enough, and declined to light. Good. A gas heater running without flow is how heat exchangers die.
Still showing CHECK FLOW after all that? Then the restriction is somewhere you cannot see. Usually that is scale inside the heat exchanger, sometimes a pressure switch that has drifted, occasionally a plumbing fault. At that point it needs a technician with gauges, because the next step is measuring flow rather than guessing at it.
Three failed attempts to light and the heater locks out. It is a soft lockout, so it releases itself after roughly an hour, or immediately if you cut power at the breaker and restore it. That recovery is exactly what makes it dangerous to your wallet: the heater appears to fix itself, so nobody investigates.
Before you reset anything, check the two boring things:
A heater that needs resetting once is telling you something. A heater that needs resetting every week is telling you something louder, and the bill goes up the longer nobody listens.
SHORTED H2O SENSOR and OPEN WATER SENSOR both mean the same thing in practice: the heater no longer trusts what it is reading for water temperature, so it stops rather than guess. On its own that is a modest repair.
What is worth knowing is how often the cause is chewed wiring rather than a failed sensor. A heater cabinet is warm, dry and undisturbed for months at a stretch, and low-voltage sensor wiring is exactly what rodents go after. We find nests inside heaters regularly enough that opening the cabinet and looking is part of how we diagnose a sudden failure. There is more on that in what a heater that will not run is telling you.
With Jandy specifically, who does the work changes what the work costs. Warranty repairs on Jandy equipment have to go through an authorized service provider. We are one, so a warranty claim is something we handle rather than something you chase.
On Jandy equipment we install, we also carry a three-year warranty. That is worth weighing when a repair estimate starts creeping toward the cost of a replacement, because the two decisions are not really separate.
| Situation | What it usually means for you |
|---|---|
| In-warranty Jandy, covered part failed | Handled as a warranty claim through us. No chasing the manufacturer. |
| In-warranty Jandy, failure caused by flow or chemistry | Often not covered, because the heater did not fail on its own. Worth knowing before the visit. |
| Out-of-warranty Jandy, wear part | Ordinary repair |
| Out-of-warranty Jandy, heat exchanger gone | Replacement conversation |
Orange County water is hard, and a pool concentrates it, because every gallon that evaporates leaves its minerals behind. Those minerals build up inside the heat exchanger, narrow the passages and choke off both flow and heat transfer.
That single fact sits behind a surprising share of CHECK FLOW and HIGH LIMIT messages in this county, and it is why heaters here fault younger than the brochure suggests. It is also why a replacement without a water conversation only resets the clock. Sometimes the honest finding is that the heater is fine and the chemistry is not.
If your heater is a Pentair rather than a Jandy, the codes read differently and we have written those up too: Pentair MasterTemp error codes. For symptoms without a code, start with pool heater not working. Real numbers are on the heater repair cost page, and if you are choosing rather than repairing, there is heat pump vs. gas.
Photograph the display, and the control board light if you can get to it safely, plus the equipment pad. Tell us what it does and we will tell you what it points to before anyone drives out.
Get a Free EstimateACE Pool Repair & Remodel is a licensed California pool contractor, CSLB #1075061, based at 251 E Imperial Hwy, Fullerton, CA 92835, serving Orange County since 2014. We are an authorized Jandy warranty center and we repair Pentair, Hayward and Raypak equipment as well. We do not run after-hours emergency calls. Related reading: Pentair MasterTemp error codes, pool heater not working, heater repair costs, all equipment services.
