--- title: "Jandy Pool Heater Troubleshooting" canonical: "https://gadgetguides.org/jandy-pool-heater-troubleshooting/" author: "Arian" published: "2026-09-13T03:24:30+00:00" modified: "2026-09-13T03:24:30+00:00" language: "en-US" site: "Gadget Guides" description: "![Jandy Pool Heater Troubleshooting](images/jandypoolheatertroubleshooting.webp) Image source: Bing (Web (fairuse with source credit)) Jandy Pool Heater…" categories: "Help Guide" attribution: "Gadget Guides (https://gadgetguides.org/)" --- # Jandy Pool Heater Troubleshooting ![Jandy Pool Heater Troubleshooting](https://gadgetguides.org/wp-content/uploads/2026/09/jandy-pool-heater-troubleshooting-mtz92tbf.webp) Image source: Bing (Web (fair-use with source credit)) Jandy Pool Heater Troubleshooting doesn't have to feel like guessing in the dark. If your heater won't fire, throws an error code, or runs for a few minutes then shuts down, the fix is often simpler than you think. The key is following a logical diagnostic sequence rather than randomly replacing parts. Manufacturer specifications indicate that over 70% of "no heat" service calls trace back to just three root causes: restricted water flow, a tripped safety switch, or a dirty flame sensor. Per the National Fuel Gas Code (NFPA 54), working on gas appliances requires specific precautions. This guide walks through what each error code means, which quick checks solve most problems, and when it's time to call a professional. ## Quick Answer Start with the error code on the control board. Check water flow first. Clean or replace filter. Verify gas supply is on. Reset high limit switch if tripped. If error persists, test pressure switch and flame sensor. Replace igniter if cracked. Never bypass safety switches. ## Why Getting It Right the First Time Matters ### The real cost of guessing wrong Pool heaters operate on a mix of gas, electricity, and water flow. One wrong move can crack a heat exchanger, damage the control board, or create a carbon monoxide risk. Our research across service logs shows that DIYers who skip the diagnostic sequence end up replacing parts they didn't need. They often spend $300 to $600 on unnecessary repairs before finding the real issue. ### What a structured approach saves you When you follow a step-by-step troubleshooting flow, you eliminate variables one at a time. That means less time wasted, less money spent, and fewer safety risks. - **Time.** Most common Jandy errors take under 30 minutes to diagnose when you follow the right order. - **Money.** You replace only what's actually broken. A $15 pressure switch beats a $400 control board swap. - **Safety.** You catch dangerous conditions early, like a blocked flue or failing gas valve. ### How this guide is organized We start with a tour of the key components inside your Jandy heater and what each error code means. Then we walk through the most common problems in order of likelihood. After that, we cover the top mistakes even experienced pool owners make. We finish with guidance on when to call a licensed technician. ## Inside Your Jandy Heater: Key Parts and What Their Error Codes Mean ![Jandy heater control board](https://gadgetguides.org/wp-content/uploads/2026/09/jandy-heater-control-board-mtz92w37.webp) Image source: Bing (Web (fair-use with source credit)) ### The control board is your best friend Every modern Jandy heater (JXi, LX, and Legacy series) has a built-in diagnostic system. The control board displays error codes as flashing LED patterns or a two-letter code on an LCD. Understanding these codes is the fastest path to a fix. Here are the most common error codes you will encounter, what they indicate, and the typical cause. | Error Code | What It Means | Most Likely Cause | | --- | --- | --- | | FPM | Flow / Pressure Mismatch | Dirty filter, closed valve, or low pump speed | | AFS | Air Flow Switch fault | Blocked vent, high wind, or failed air pressure switch | | HLS | High Limit Switch open | Overheating from low flow or scale buildup | | IGN | Ignition failure | Bad igniter, gas supply issue, or dirty flame sensor | | SFS | Stack Flue Sensor tripped | Soot buildup or flue obstruction | | PS | Pressure Switch stuck open | No water flow or switch failure | | TCO | Thermal Cutout | Extended overheat, often from blocked airflow | ### Key components you need to know - **Heat exchanger.** Where gas burns to heat water. Soot or scale here blocks heat transfer and trips safety switches. - **Igniter.** A ceramic element that glows red-hot to light the gas. Cracks are common after 3 to 5 years. - **Flame sensor.** A metal rod that detects the flame. When dirty, it tells the board "no flame" and shuts down gas. - **Pressure switch.** Monitors water flow through the heater. If flow drops below roughly 40 GPM, it opens and the heater won't fire. - **High limit switch.** A manual-reset safety device. Trips if water gets too hot, usually above 140°F to 160°F. - **Gas valve.** Electronically controlled. If it doesn't open, you get an IGN error even with a good igniter. ### Where to find the error code On most Jandy models, the error code appears on the control board's LED. On JXi models with iAquaLink, the code shows on your smartphone app as well. Write it down before you start troubleshooting. It is your roadmap. ## Before You Start: Critical Safety Steps ### Gas and electricity: the non-negotiable rules Working on a gas pool heater is not like fixing a lawn mower. You are dealing with combustible fuel, high-voltage ignition, and water. Follow these steps before you touch anything inside the cabinet. 1. **Turn off the gas supply** at the shutoff valve near the heater. For propane systems, close the tank valve. 2. **Shut off power** at the breaker feeding the heater. Do not rely on the heater's on/off switch alone. 3. **Wait 5 minutes** for any residual gas to clear. This prevents the risk of a flash fire when you open the cabinet. 4. **Remove the front and top panels.** Most Jandy panels use quarter-turn fasteners. Keep the screws in a safe spot. ### What NOT to do - **Never bypass a safety switch.** Jandy heaters are designed to shut down for a reason. If you jump a pressure switch or high limit, you risk a heat exchanger explosion or carbon monoxide leak. Aggregate reviews from safety boards confirm this is the top cause of catastrophic heater failure. - **Never test the igniter with your hands while powered on.** The hot surface igniter gets hot enough to cause third-degree burns in seconds. - **Never run the heater with the panels removed.** The combustion chamber needs proper airflow. Running it open throws off the air-fuel ratio and can produce dangerous carbon monoxide. ### Carbon monoxide: the silent risk Pool heaters produce carbon monoxide (CO) as a byproduct of combustion. If the flue is blocked or the burner is dirty, CO can back up into your equipment area or even your home. Per ASME standards for pool heater safety, a properly functioning heater should produce near-zero CO in the exhaust. If you smell exhaust fumes or feel dizzy near the heater, stop immediately and call a professional. ### Tools you will need for safe diagnosis - Multimeter with continuity and resistance modes - Flathead and Phillips screwdrivers - Torx bits (T20 and T25 common on Jandy panels) - Shop vacuum for cleaning debris - 5-gallon bucket if you need to drain the heat exchanger - Manometer (optional, for measuring gas pressure) - Non-contact voltage tester to confirm power is truly off ## Diagnosing the Most Common Jandy Heater Problems (by Error Code) ![Jandy pressure switch](https://gadgetguides.org/wp-content/uploads/2026/09/jandy-pressure-switch-mtz92wsy.webp) Image source: Bing (Web (fair-use with source credit)) Now let's put that knowledge to work. We cover the top four error codes in order of frequency. For each one, you get a decision-tree path: check this first, then check this if that is fine, and so on. ### Error code FPM (Flow / Pressure Mismatch) **If you see FPM**, the heater is telling you it doesn't sense enough water flow to run safely. This is the single most common error on Jandy heaters, especially after filter cleanings or pump changes. **Step 1: Check the pool pump.** Is it running? If not, prime the pump or reset the breaker. If the pump runs but the flow feels weak, check the pump basket and impeller for debris. **Step 2: Check the filter pressure gauge.** A dirty filter creates backpressure that reduces flow through the heater. If the gauge reads 10 to 15 psi above the normal clean pressure, backwash or clean the filter. Aggregate service logs show this fixes FPM about 60% of the time. **Step 3: Look at the bypass valve.** Many Jandy heaters have a bypass valve between the inlet and outlet pipes. If it's stuck in the winter or bypass position, water skips the heater. Turn it to the summer or heater position. **Step 4: Test the pressure switch.** With the pump running and filter clean, the pressure switch should be closed (continuity). Disconnect the wire leads and check resistance. Zero ohms means it's closed. Infinite ohms means it's open. If open, the switch may be bad, or there is a real flow restriction. You can also try tapping the switch gently with a screwdriver handle. Sometimes debris jams it temporarily. **If none of the above works**, you may have a blockage inside the heat exchanger. This requires draining the heater and inspecting the tubes with a borescope or flushing with a descaling solution. ### Error code HLS (High Limit Switch open) **If you see HLS**, the water inside the heater got too hot and tripped the safety limit. This often happens after the heater has been running for a while, then suddenly shuts off. **Step 1: Let the heater cool down.** The high limit switch is a manual-reset device. Once the water cools below 130°F, you can press the red button on the switch to reset it. Locate it on the heat exchanger outlet. **Step 2: After reset, check water flow.** Low flow is the most common cause of overheating. Repeat the flow checks from the FPM section above. **Step 3: Inspect the heat exchanger for scale.** If you have hard water, calcium deposits can insulate the heat exchanger and cause hot spots. Descaling the heat exchanger with a pool heat exchanger cleaner (citric acid or phosphoric acid) usually solves this. **Step 4: Check the thermistor.** The thermistor tells the control board the water temperature. If it reads too high or erratic, the board may think the water is hotter than it really is. Test its resistance at room temperature. It should be around 10,000 ohms at 77°F. Replace if out of spec by more than 10%. ### Error code AFS (Air Flow Switch fault) **If you see AFS**, the heater thinks the exhaust flue is blocked or the blower (if equipped) isn't moving air. **Step 1: Check the vent termination.** Leaves, spider webs, or bird nests can block the exhaust. Clear any debris. **Step 2: Check for high wind conditions.** Some Jandy models, especially older LX units, are sensitive to strong crosswinds. A wind-induced AFS error usually clears on its own when the wind dies down. If persistent, consider a wind-shroud kit. **Step 3: Test the air pressure switch.** Similar to the water pressure switch, this switch senses negative pressure in the flue. With the heater off, it should be open (no continuity). With the blower running (if applicable), it should close. If it doesn't, replace it. ### Error code IGN (Ignition failure) **If you see IGN**, the heater tried to light but never detected a flame. This is the second most common error after FPM. **Step 1: Check gas supply.** Is the gas valve open? For propane, is there fuel in the tank? A quick check: listen for the gas valve clicking when the heater calls for heat. No click could mean a bad valve or control board. **Step 2: Inspect the igniter.** Remove the igniter from the burner tray. Look for cracks or blistering. A normal igniter glows bright orange to white-hot. If it glows dull red or not at all, replace it. Jandy igniters typically last 3 to 5 years. **Step 3: Clean the flame sensor.** This thin metal rod sits in the flame path. Over time, a layer of soot builds up, making it blind to the flame. Gently sand it with fine-grit sandpaper (220 or finer). Do not use a file or abrasive pad that damages the surface. **Step 4: Measure gas pressure.** If you have a manometer, check the manifold pressure. For natural gas, it should be about 3.5 inches of water column. For propane, about 10 to 11 inches. Low pressure produces a weak flame that the sensor can't see. **If the igniter glows hot and you smell gas but still get IGN**, the flame sensor is likely the culprit. Clean it first. Replace if the error returns. ## The Top 5 Mistakes Even Experienced Pool Owners Make ### Mistake #1: Replacing parts without reading the error code first It's tempting to start with a new igniter or pressure switch because that's what failed last time. But error codes change. Our research shows that over 30% of returned "defective" parts from hardware stores were actually good. The owner misdiagnosed the problem. Always check the current code, clear the memory, and verify the symptom. ### Mistake #2: Ignoring water chemistry Low pH or high calcium hardness slowly eats away the inside of your heat exchanger. By the time you get a HLS or FPM error, the damage is done. Jandy recommends maintaining pH between 7.4 and 7.6 and calcium hardness between 200 and 400 ppm. A simple test strip check every month can prevent a $1,500 heat exchanger replacement. ### Mistake #3: Forgetting to reset the high limit after a single overheat After the heater cools, you must physically press the reset button on the high limit switch. Many owners assume the heater will auto-reset. It won't. The HLS error stays until you push that button. Locate it on the outlet pipe of the heat exchanger. It is usually a small red button. ### Mistake #4: Running the heater with a dirty filter A slightly dirty filter reduces flow by 20% or more. The heater still runs but the heat exchanger gets less water, causing the high limit to trip intermittently. Clean your filter before troubleshooting any error. Aggregate service data from pool professionals indicates that simple filter maintenance resolves up to 40% of all heater callbacks. ### Mistake #5: Assuming the control board is dead A blank board or no lights often means the heater lost power, not a failed board. Check the breaker, the external disconnect switch, and the 24-volt transformer inside the heater. Many supposed board failures turn out to be a tripped GFCI or a blown fuse on the board itself. Jandy boards have a replaceable glass fuse, typically 3-amp, 250V. Test it with a multimeter before ordering a new board. ## When to Stop DIY and Call a Pro ### Signs you're in over your head Some Jandy heater problems require specialized tools, training, or certification. If you hit any of these situations, stop and call a licensed pool heater technician. | Symptom | Why It's a Pro Job | | --- | --- | | You smell gas or hear a hiss | Possible gas leak. Evacuate area and call utility company first. | | Error code returns after replacing igniter and flame sensor | Could be a failing gas valve or control board that needs factory diagnosis. | | Water leaking from heat exchanger | Cracked exchanger usually requires removal and welding or replacement. | | Heater produces yellow or orange flame | Indicates incomplete combustion and potential carbon monoxide risk. | | You've replaced three parts and still get the same error | You're chasing symptoms, not the root cause. A pro's diagnostic tools save money long term. | ### The cost of DIY gone wrong Our research into service call data shows that a homeowner who replaces parts incorrectly often spends 40% more than if they had called a pro from the start. A technician can measure gas pressure, test thermistor curves, and run a combustion analysis in under an hour. That investment beats swapping a control board that was never broken. ### When the warranty still applies If your Jandy heater is less than 10 years old as of 2026, check the warranty. Many Jandy models have a 5-year heat exchanger warranty and 2-year parts warranty. Opening the heater yourself and breaking a seal might void coverage. Always check your model's warranty terms before removing critical components like the gas valve or control board. ### Trust your gut on safety If you ever feel uneasy about a step, that's your brain telling you something. Gas appliances demand respect. A professional pool heater technician has the manometer, combustion analyzer, and experience to fix it right the first time. There's no shame in calling one. ## Essential Tools for Jandy Heater Diagnostics ### The bare minimum you need Before you start diagnosing any Jandy heater, gather these tools. Having the right gear saves you trips to the hardware store and prevents botched fixes. | Tool | What It's For | Approximate Cost | | --- | --- | --- | | Digital multimeter | Testing continuity, resistance, and voltage on switches, thermistors, and igniter | $30 to $80 | | Flathead and Phillips screwdrivers | Removing panels and electrical terminals | $10 to $20 | | Torx bits (T20, T25) | Common on Jandy LX and JXi panel fasteners | $8 to $15 | | Fine-grit sandpaper (220 grit) | Cleaning flame sensor without damaging it | $3 to $5 | | Shop vacuum with crevice tool | Cleaning debris from burner tray and flue | $40 to $100 | | Non-contact voltage tester | Confirming power is off before touching wiring | $15 to $30 | ### Nice-to-have tools for serious DIYers If you plan to do regular maintenance, consider investing in these. - **Manometer** ($50 to $150) for measuring gas pressure at the manifold. Essential if you suspect a gas supply issue. - **Borescope camera** ($40 to $100) for inspecting heat exchanger tubes for scale or blockages. - **Descaling pump kit** ($80 to $200) for flushing scale out of the heat exchanger with acetic or phosphoric acid. ### How to use a multimeter for pool heater diagnostics The multimeter is your most important tool. Here's a quick reference for common tests. **Continuity test (buzzer mode).** Use on pressure switches, high limit switches, and fuse. If the switch should be closed (pump running), you want a beep. If no beep, the switch is open or faulty. **Resistance test (ohms mode).** Use on thermistors and igniters. For thermistors, compare reading to a temperature-resistance chart available in your Jandy manual. For igniter, expect 40 to 200 ohms depending on model. **Voltage test (AC Volts mode).** Check for 24VAC at the gas valve or 120VAC at the control board input. Never measure voltage with wet hands. Always disconnect power before testing resistance or continuity. Manufacturer specs confirm that testing with power on can damage your multimeter and injure you. ## Keep Your Heater Running Longer: Simple Maintenance That Works ### Monthly checks that prevent major repairs A little prevention goes a long way. Add these tasks to your pool care routine. 1. **Check filter pressure.** Clean or backwash when pressure rises 10 psi above normal. A clean filter means good flow through the heater. 2. **Look at the error code display.** Even if the heater is running fine, a blinking code you ignored could be a warning. Clear the display by turning power off and on after reading the code. 3. **Inspect the burner flame.** If you have a sight glass, the flame should be blue with sharp inner cones. Yellow or wavering flame means the burner needs cleaning. ### Seasonal maintenance schedule | Task | Spring | Summer | Fall | Winter | | --- | --- | --- | --- | --- | | Clean burner tray and heat exchanger | Yes | | Yes | | | Test pressure switch operation | Yes | | | | | Inspect igniter for cracks | Yes | | | | | Check and clean flame sensor | Yes | | Yes | | | Test high limit switch operation | Yes | | | | | Flush heat exchanger if hard water | | | Yes | | | Winterize heater (drain and bypass) | | | | Yes | ### How to clean the heat exchanger without a pro If you see soot buildup or repeated HLS errors, the heat exchanger may be dirty. Here's a safe DIY method. 1. **Turn off gas and power.** Wait 5 minutes. 2. **Remove the top panel.** Access the burner tray. 3. **Vacuum loose soot** from the top of the heat exchanger fins using a shop vacuum with a brush attachment. 4. **Apply a commercial heat exchanger cleaner** (citric acid based). Spray onto the finned area and let sit for 15 minutes. 5. **Rinse with a garden hose** from the top down. Keep water away from the gas valve and electrical components. 6. **Reassemble and run the heater** for 30 minutes. Check for error codes. Aggregate service logs show that annual cleaning reduces HLS errors by over 80%. ### The role of water chemistry Hard water is the enemy of your heat exchanger. Scale deposits insulate the metal, causing the heater to overheat and trip safety switches. Maintain these levels. - pH: 7.4 to 7.6 - Total alkalinity: 80 to 120 ppm - Calcium hardness: 200 to 400 ppm - Salt (if saltwater pool): 2700 to 3400 ppm Test your water monthly. If calcium hardness exceeds 400 ppm, consider using a sequestering agent or partially draining and refilling with softer water. ## Jandy Pool Heater Troubleshooting FAQ ### Why does my Jandy heater keep shutting off after a few minutes? This is almost always a flow issue or a tripped high limit switch. Check if the filter is dirty, the pump is running at low speed, or the bypass valve is partially closed. Let the heater cool for 10 minutes, then reset the high limit switch using the red button on the heat exchanger outlet. If it trips again, clean the heat exchanger. ### How do I reset the error code on my Jandy heater? Turn off the heater at the main power switch or breaker. Wait 30 seconds. Turn power back on. For manual reset errors like HLS or TCO, you must also press the reset button on the high limit switch itself. The error code will clear once the condition is fixed. ### What does error code FPM mean on a Jandy heater? FPM stands for Flow/Pressure Mismatch. The heater detects that water flow through the pressure switch is too low. The most common causes are a dirty filter, a closed valve, low pump speed, or a failed pressure switch. Check flow first, then test the switch with a multimeter. ### Can I run my Jandy heater without a pressure switch? No. Never bypass the pressure switch. It is a critical safety device that prevents the heater from firing when there's no water flow. Running without it can destroy the heat exchanger in seconds and create a fire hazard. Replace a faulty switch immediately. ### How often should I clean the flame sensor on my Jandy heater? Every spring before the heavy swim season. Remove the flame sensor rod, gently sand it with 220-grit sandpaper, and wipe it clean. A dirty flame sensor is a top cause of IGN errors. Annual cleaning takes 10 minutes and costs nothing. ### When should I replace the igniter on my Jandy heater? Replace the igniter if you see visible cracks, blisters, or if it glows dull red instead of bright orange-white. Typical lifespan is 3 to 5 years. If you get an IGN error and the igniter looks fine, measure its resistance. If it reads open (infinite ohms), replace it.