Jandy's gas heaters and heat pumps don't use numbered codes. When something is wrong, the display spells out a fault, like CHECK FLOW or FAULT- HIGH LIMIT. That makes them easier to read than most, but the message alone doesn't tell you whether it's a dirty filter or a failed part. This guide goes through every fault in Jandy's manuals for the JXi and LXi gas heaters and the VersaTemp heat pump, what Jandy says causes it, and what you can safely check.

If you have a Hayward or Pentair heater, see our Hayward heater code guide or Pentair MasterTemp code guide.

Safety first

If you smell gas, leave the area and call your gas supplier from a neighbor's phone, before anything else. Jandy's instructions are specific: don't try to light any appliance, don't touch any electrical switch, don't use any phone in the building, and if you can't reach your gas supplier, call the fire department (JXi manual, p. 1; LXi manual, p. 1).

Everything in this guide is done from outside the heater's cabinet. Jandy says its heaters must be serviced only by a qualified professional service technician, because service involves fuel gas, electricity, moving parts and testing or bypassing safety controls (JXi manual, p. 48; LXi manual, p. 44). If a heater keeps tripping its breaker, leave the breaker off and call.

Before you look up the code

Jandy's own list of things to confirm before calling for service is short, and it catches a lot (LXi manual, p. 44; JXi manual, p. 48):

The heater is set to POOL or SPA, and that setpoint is higher than the water temperature.
The pump is running, the filter and all the baskets are clean, and no valve is in the wrong position.
The gas and electric supplies are on, and any time clock is set correctly.
Nothing is blocking the heater's exhaust vent or air intake.

A lot of Jandy heater faults are about water flow. Both gas heaters need at least 30 gallons per minute through them (JXi manual, p. 24; LXi manual, p. 7), and Jandy warns that the JXi can turn off or be damaged below that.

JXi gas heater faults

From the JXi's service diagnostic messages (JXi manual, p. 47):

Display	What Jandy lists as causes	What you can check
CHECK FLOW	Pump not running; low pump pressure; pressure switch fault; variable-speed pump set too low	Breaker, wiring and time clock; clean the filter and baskets; valve positions; return eyeball fittings in place; raise the pump speed
FAULT- HIGH LIMIT	Water in the heater above its internal limit; limit switch fault	Nothing inside. Jandy's remedies are vent inspection and switch replacement by a technician
FAULT- HIGH FLUE TEMPERATURE	Flue temperature limit	Jandy says to contact a service professional
FAULT- CHECK IGN CONTROL	Air-switch tubing, fan, igniter, low gas supply, no flame at the burner	Clearances around the heater and anything blocking the flue outlet; then a technician
FAULT- SHORTED H2O SENSOR or OPEN WATER SENSOR	Wiring or connection; failed water temperature sensor	A technician
FAULT- PUMP	The filter pump is off while the heater is in Maintain Temp mode	Nothing. Jandy says this is normal and needs no service

CHECK FLOW is the one to start with. On the JXi, a water pressure switch at the header inlet senses whether water is reaching the heater, and if it doesn't sense enough, the heater shows CHECK FLOW and stops (JXi manual, p. 7). Jandy names a variable-speed pump set too low as a cause. A quiet, low-speed program can run all day without moving enough water for the heater. If the heater only needs to run some of the time, the pump needs a speed that meets the heater's minimum while it does. Our Pentair IntelliFlo and Hayward TriStar VS guides cover pump-side codes.

HIGH LIMIT means the water inside the heater got too hot. The JXi has two high-limit switches, one at 135°F on the heat exchanger's first pass and one at 150°F at the outlet, and either one closes the gas valve (JXi manual, p. 7). Low flow is a common way to get there. Jandy's troubleshooting table also lists pounding or knocking with low flow, a failed thermal regulating valve, a damaged internal bypass, a variable-speed pump set too low, and a dirty filter or baskets (JXi manual, p. 46). For heaters that cycle on and off, see why a pool heater keeps turning on and off.

JXi ignition control LED

Inside the heater, the ignition control has an LED that flashes its own codes (JXi manual, p. 48):

On continuously: ignition control fault.
One flash: air flow fault.
Two flashes: flame present with no call for heat.
Three flashes: ignition lockout after three failed attempts to fire.

The JXi tries to light three times before it shows an ignition fault (JXi manual, p. 7). The LED sits inside the cabinet, so reading it is technician work.

LXi gas heater faults

The LXi's messages are similar, with one name change and one extra fault (LXi manual, p. 43):

Display	What Jandy lists as causes	What you can check
NO FLOW	Pump not running; low pump pressure; pressure switch fault	Breaker, wiring and time clock; clean the filter; clear any blockage; valve positions
FAULT- HIGH LIMIT	Water in the heater above its internal limit; limit switch fault	A technician (temperature rise test, switch checks)
FAULT- FUSELINK/FIELD	The roll-out (fusible link) switch or the vent temperature limit has opened	A technician. Don't reset it repeatedly
FAULT- CHECK IGN CONTROL	Fan tubing, fan, restricted air flow, oscillating pump pressure, low gas supply, no flame	Clearances and vent; clean the filter (Jandy's remedy for oscillating pump pressure); then a technician
FAULT- SHORTED H2O SENSOR or OPEN WATER SENSOR	Wiring or connection; failed sensor	A technician
FAULT- PUMP	Pump off while in Maintain Temp mode	Nothing. Normal

NO FLOW is the LXi's version of CHECK FLOW, and the same checks apply. FUSELINK/FIELD is one to take seriously: it means a roll-out switch or the vent temperature limit has opened, both safety devices, and Jandy's remedy for each is a technician finding the cause and correcting the connection or replacing the switch (LXi manual, p. 43).

The LXi's ignition control LED uses the same four patterns as the JXi: on continuously, one, two or three flashes (LXi manual, p. 41).

VersaTemp heat pump faults

The VersaTemp is a heat pump, so it has refrigerant pressure faults instead of ignition faults. From Jandy's diagnostics and troubleshooting tables (VersaTemp manual, pp. 26-27):

Display	What it means	What you can check
FAULT- NO FLOW	Low or restricted water flow; external bypass valve in the wrong position; or a failed water flow switch	Pump on; valves set correctly; clean filter and skimmers; pool water level; temporarily turn off fountains or waterfalls that bypass the heat pump
FAULT- HIGH REF PRESSURE	Refrigerant head pressure too high; the compressor stops until the switch resets	Same flow checks, and if you have a two-speed or variable-speed pump, a higher speed. After a long idle period, Jandy says to cycle the heat pump off and on up to three times
FAULT- LOW REF PRESSURE	Suction pressure too low, which Jandy notes can happen when the air is cold	Is the fan running and air coming out of the top? If the heat pump won't run at all, call
FAULT- HIGH WATER TEMP	Pool or spa water at or above the maximum allowed temperature	Nothing at the pad. Jandy says the control shuts the heat pump off to protect anyone in the water, even when a remote thermostat is calling for heat
FAULT- SHORTED or OPEN COIL SENSOR	Coil temperature sensor failed or disconnected	A technician
FAULT- SHORTED or OPEN WATER SENSOR	Water temperature sensor failed or disconnected	A technician

The VersaTemp needs a minimum of 20 gallons per minute on the 2000R and 2500R and 30 on the 3000R models, with a maximum of 70 (VersaTemp manual, p. 6).

Not running, but no fault? The control waits five minutes after the water falls below the setpoint before it starts the heat pump (VersaTemp manual, p. 20), and Jandy's troubleshooting table lists that delay first when the display works but the unit won't start (VersaTemp manual, p. 26). Make sure it isn't set to cooling.

Water under the heat pump? Heat pumps make condensation. Jandy's test is to turn the heat pump off, then the circulating pump off for at least an hour: if the water stops, it's normal condensation; if it keeps coming, call for service (VersaTemp manual, p. 26).

Where to stop

The faults that come from flow (CHECK FLOW, NO FLOW, and often HIGH LIMIT and HIGH REF PRESSURE) are worth a look at the pump, filter, baskets and valves first. FAULT- PUMP in Maintain Temp mode isn't a fault at all. Everything else on this page, the sensor faults, ignition faults, FUSELINK, flue and refrigerant faults, is inside the cabinet and belongs to a technician. Don't keep clearing a fault that comes back.

Getting it diagnosed

Call when a flow fault comes back after the filter is clean and the pump is on a speed that meets the heater's minimum, or when the heater shows any of the inside-the-cabinet faults above. Our heater diagnostic checks the flow, the pressure switch and limits, reads the fault against Jandy's manual, and tells you what has failed and what putting it right involves before anything is quoted.

If you don't know what's wrong, a diagnostic is $120, and it's credited toward your repair if you go ahead. Start from pool heater repair or heat pump repair, or answer a few questions in the Pool Problem Finder. A photo of the display and the heater's rating plate helps. For a heater with no fault that just isn't warming the water, see why your pool heater isn't heating.

Sources

Every manufacturer statement above links to this list. Page numbers are the printed page numbers in each manual.

Zodiac Pool Systems (Jandy), JXi Gas-Fired Pool and Spa Heater Installation and Operation Manual, H0574300 Rev M (2024).
Zodiac Pool Systems (Jandy), LXi Gas-Fired Pool and Spa Heater Installation and Operation Manual, H0286900 Rev T.
Zodiac Pool Systems (Jandy), VersaTemp JRT Series Heat Pump Installation and Operation Manual, H0744700 Rev H.

Jandy, JXi, LXi and VersaTemp are trademarks of Zodiac Pool Systems. They are named here only to identify equipment.

Jandy pool heater error codes: JXi, LXi and VersaTemp