April 15, 2026
Equipment Repair & Troubleshooting
In This Guide
- What Is an Ignition Lockout?
- Start Here: The 80/20 Rule
- Tools You’ll Need Before You Start
- Error Codes by Brand: What They Mean
- Fix #1: Restore Water Flow (Works for All Brands)
- Brand-Specific Fixes and Replacement Parts
- DIY vs. Professional: Know the Line
- Prevention: Keep Your Heater Running Year-Round
- Water Chemistry That Protects Your Heater
- Frequently Asked Questions
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What Is an Ignition Lockout?
An ignition lockout is your heater’s way of hitting the brakes before something dangerous happens. When the heater’s control board initiates a startup sequence — opening the gas valve, energizing the igniter, and confirming flame — it’s running through a rapid series of safety checks. If any one of those checks fails at the wrong moment, the board cuts the gas and locks out the ignition system.
This isn’t a malfunction. It’s the safety system doing exactly what it was designed to do: prevent unignited gas from accumulating in the combustion chamber. An ignition lockout protects you, your family, and your equipment. The challenge is figuring out why the check failed — because the causes range from a $0 cleaning job to a $350 control module replacement.
⚠️ Before You Start
Turn off the heater at the breaker and let it cool for at least 15 minutes before inspecting any internal components. Never attempt to open gas connections, adjust manifold pressure, or bypass a safety switch. Those tasks require a licensed professional.
Start Here: The 80/20 Rule
Here’s the most useful thing a pool technician will ever tell you before charging you a service call fee:
70–90%
of all heater service calls are caused by water flow issues — not the heater itself. Check your filter and baskets first.
The heater requires sufficient water pressure to close its internal pressure switch before it will attempt to fire. No flow — or insufficient flow — and the safety system locks it out immediately. The heater isn’t broken. It’s waiting for water.
Before you do anything else, run through this four-item external checklist. If any one of these is off, fix it first and try the heater again:
- Dirty filter or clogged pump/skimmer baskets — the single leading cause of ignition failure
- Thermostat set point — must be at least 2°F above the current water temperature
- Valves — confirm all suction and return valves are fully open
- Power and fuel supply — check the circuit breaker and confirm the gas line is on
Pro Tip
If you have a variable-speed pump, a common culprit is that the pump is running on a low-speed schedule during the heater’s firing window. The pressure switch won’t close at low RPM. Bump the pump to its highest speed before troubleshooting the heater itself.
Tools You’ll Need Before You Start
If the basic flow checks don’t resolve the lockout, you’ll need some equipment to properly diagnose internal issues. Don’t guess — these tools tell you exactly what’s wrong so you don’t spend money replacing the wrong part.
| Tool | What It Measures | Why You Need It |
|---|---|---|
| Multimeter | 24VAC, 120/240VAC, DC millivolts, microamps (μA) | Checks gas valve voltage, flame current, switch continuity |
| Manometer | Gas pressure in inches of water column (wc) | Diagnoses low gas pressure under load (requires licensed tech) |
| Handheld Mirror | Visual inspection | Safely view burner flame and check for heat exchanger leaks |
| 7/32″ Allen Wrench | Mechanical adjustment | Water pressure switch calibration |
| Contact Thermometer | Water temperature (°F) | Temperature rise tests and thermal regulator valve diagnostics |
Error Codes by Brand: What They Mean
Each manufacturer has its own diagnostic language. Knowing exactly what your error code means is the difference between a targeted repair and an expensive guessing game. Here’s the complete breakdown for each major brand.
Hayward systems use a digital display to report exactly which part of the safety loop is open. The display codes are precise — each one points to a specific subsystem.
| Code | Meaning | Most Common Causes |
|---|---|---|
| IF | Ignition Failure | 1. Clogged orifices (spider nests) 2. Bad flame sensor 3. Low gas pressure |
| LO | Limit String Open | 1. Low water flow 2. High limit switch tripped 3. Pressure switch open |
| HF | High Flame Sensed | 1. Flame detected with gas valve off 2. Faulty ICB board |
| AO | Air Switch Open | 1. Blower failure 2. Loose vacuum tubing 3. Blocked vent |
Key measurement: During an ignition trial, check for 22–28VAC at the gas valve. Standard millivolt pilot generators should read 700–750mV (no load) and require a minimum of 600mV to hold the valve open.
Pentair units use Fenwal ignition modules with a secondary set of diagnostic LEDs on the back of the board. Pay attention to both the main display and those LEDs — together they give you the full picture.
| Code | Meaning | Most Common Causes |
|---|---|---|
| ERR IGN (3 LED flashes) | Ignition Lockout | 1. Faulty HSI igniter 2. Weak flame current 3. Gas supply volume too low |
| ERR PS | Pressure Switch Open | 1. Clogged filter 2. Internal bypass broken 3. Switch out of adjustment |
| ERR HLS | High Limit Switch | 1. Insufficient water flow 2. Scale in heat exchanger 3. Bad Thermal Regulator Valve |
| ERR SFS | Stack Flue Sensor | 1. Sooted heat exchanger 2. Low flow 3. Failed sensor |
Key measurement: Measure HSI resistance — it should read approximately 50 ohms. Flame current must be between 1.0 and 10 μA to maintain operation. The gas regulator is factory-set to −0.2″ wc below blower inlet air pressure.
Jandy (Fluidra) units display “Service Codes” with descriptive text. Grounding issues are unusually common on JXi models due to their design — if your JXi keeps showing FL 2, the ground circuit is the first thing to investigate, not the igniter itself.
| Code | Meaning | Most Common Causes |
|---|---|---|
| FL 2 / CHECK IGN | Failed Ignition | 1. Corrosion in grounding circuit 2. Broken sensing wire 3. EMI/ground interference |
| CHECK FLOW | Low Water Flow | 1. Clogged baskets/filter 2. Pump speed too low 3. Faulty switch |
| FAULT-HIGH LIMIT | Overheating | 1. Bad Thermal Regulator Valve (TRV) 2. Closed bypass valve 3. Blocked tubes |
| FAULT-FUSELINK | Roll-out Switch Tripped | 1. Flames exiting the front (flame rollout) 2. Sooted heat exchanger |
Key measurement: Flame sensing signal must not fall below 1.5 microamps. Igniter resistance: 40–90 ohms (JXi) or 40–75 ohms (Legacy). Code 144/145 on hybrid Jandy systems indicates salinity out of range (<2.0 or >4.0 gpl).
Fix #1: Restore Water Flow (Works for All Brands)
Regardless of what error code is displayed, perform these four steps first. This resolves the majority of ignition lockouts with zero parts cost and under 30 minutes of your time.
Clean the Pump and Skimmer Baskets
Remove and empty both the pump strainer basket and the skimmer basket. Even a partially blocked basket at high season can reduce flow enough to prevent the pressure switch from closing. Rinse with a hose if needed and reinstall securely.
Backwash or Clean the Filter
For sand or DE filters, run a full backwash cycle. For cartridge filters, remove and rinse the element. The filter pressure gauge should drop back to its “clean” baseline reading. A filter running 8–10 PSI over its clean starting pressure is starving the heater of water.
Verify All Valves Are Fully Open
Walk your plumbing line. Confirm that every suction valve and every return valve is turned fully open. A single partially-closed valve on the suction side can drop flow enough to trigger a lockout. Check valves that direct flow to the heater specifically.
Raise Pump Speed and Retry
If you have a variable-speed pump, set it to maximum RPM. Power the heater on. The pressure switch needs adequate flow to close. Once the heater fires successfully, you can dial the pump speed back to the minimum needed to keep the switch satisfied.
ℹ️ Cost and Time
These four steps cost $0 and take 15–30 minutes. If they resolve the lockout, you just avoided a $150–$300 service call.
Brand-Specific Fixes and Replacement Parts
If restoring water flow didn’t solve it, the problem is internal. Here’s exactly what to do for each brand — including real part numbers so you can order the right component on the first try.
Error Code LO — Limit String Open
Fix: Adjust or replace the Water Pressure Switch (part FDXLWPS1930). With the pump running at high speed and a clean filter, use a multimeter to check continuity across the switch. If it remains open under pressure, the switch is faulty. Cost: ~$50–$75 DIY vs. $200+ professional.
Error Code IF — Ignition Failure
Fix: Turn off the gas. Remove the burner manifold and inspect the far-left orifice for spider nests — this is the most common cause. Use a paper clip to clear any webbing or debris without enlarging the orifice. If the heater lights briefly then shuts down, replace the Flame Sensor (part IDXLFLS1930). Cost: $0 for cleaning, ~$40 for the sensor.
Error Code 10 — Igniter Open
Fix: Replace the Igniter (part FDXLIGN1930). Remove the igniter access cover, disconnect the plug, and remove the two securing screws. Handle the ceramic element carefully — do not touch the element with bare hands. Oil from skin causes hot spots that crack the igniter prematurely. Cost: ~$60–$100 DIY.
ERR IGN — Ignition Lockout
Fix: First, measure HSI igniter resistance — it should read approximately 50 ohms. If it reads open circuit (OL), replace the HSI Igniter (part 77707-0054, ~$60). If the igniter glows orange but the burner doesn’t fire, check for 24VAC at the gas valve terminals. If voltage is absent when it should be present, replace the Ignition Control Module (part 476224, ~$350).
ERR SFS — Stack Flue Sensor
Fix: This sensor trips when exhaust exceeds 480°F — usually caused by a sooted or scaled heat exchanger restricting gas exhaust. If the sensor itself reads as an open circuit (E05/E06 on the Fenwal board), replace the Stack Flue Sensor (part 42002-0024S, ~$70). Unscrew from the exhaust elbow and install the new one.
ERR PS — Pressure Switch
Fix: With the pump running, turn the pressure switch adjustment dial counter-clockwise in small increments until the error clears. If it won’t adjust or the switch is cracked, replace it. Note: if the filter is clean and you still need to reduce pressure switch sensitivity, that’s a sign your flow is marginal — investigate the pump and plumbing next.
FL 2 / CHECK IGN — Failed Ignition
For JXi models: Poor grounding is the most frequent culprit — it prevents the Fenwal module from reading the microamp flame signal. The field fix: strip 1 inch of wire, slide it into the blower flange gap, and connect the other end to the control panel ground wires. This is an official field-documented repair. For LXi models, try cleaning the flame rod by rubbing it lightly with a dollar bill to remove oxidation. If neither works, replace the Flame Sensor Rod (part R0458601, ~$45). Cost: $0 to $45.
FAULT-FUSELINK — Roll-out Switch
Fix: Replace the Fusible Link (part R0012200, ~$30). This wax-pellet switch trips when cabinet temperatures exceed 305°F — a sign of flame rollout (flames exiting the front of the combustion chamber). Before replacing, clear the burner tray of any leaves, acorns, or debris that may be causing abnormal flame behavior. If rollout is happening without debris, the heat exchanger needs professional inspection for soot blockage.
FAULT-HIGH LIMIT — Thermal Regulator Valve (TRV)
Fix: The TRV is supposed to open at 120°F to allow cooler water into the heat exchanger. Test it by submerging it in a pot of hot water — it should open at that temperature. A failed TRV causes the water inside the heat exchanger to overheat and boil, triggering the high limit switch. Replace if it stays closed in hot water.
DIY vs. Professional: Know the Line
Pool heater repair is one of those areas where the line between “you can handle this” and “don’t touch that” is extremely clear. Stay on the right side of it.
✅ Safe for Homeowners
- Cleaning pump and skimmer baskets
- Backwashing / cleaning filter
- Adjusting the water pressure switch (7/32″ allen wrench)
- Clearing spider nests from burner orifices
- Replacing external sensors (thermistor, flame sensor rod)
- Replacing the HSI igniter (with basic wiring comfort)
- Cleaning the flame rod
- Clearing debris from the burner tray
🚫 Requires Licensed Professional
- All gas line connections and fittings
- Manifold gas pressure adjustment (manometer work)
- Internal high-voltage wiring repairs
- Heat exchanger inspection and cleaning
- Rodent-chewed or melted wiring harnesses
- Persistent board errors (Hayward BD or EE)
- Any repair on a heater under warranty
🚨 Never Bypass a Safety Switch
Bypassing a high limit switch, pressure switch, or roll-out switch to “get it running” can cause the heat exchanger to melt, create carbon monoxide conditions inside the unit, or cause a fire. These switches exist because the heater would destroy itself (or worse) without them. If a safety switch keeps tripping, find the root cause — don’t defeat the switch.
What to expect if you call a pro: A professional heater tune-up and diagnostic visit typically runs $150–$300. Replacing major components like an ignition control module adds $350+ in parts. Heat exchanger replacement is the most expensive scenario, often $500–$1,500, which may make a full heater replacement more economical if the unit is over 5–10 years old.
Warranty note: Improper water chemistry is the leading cause of denied warranty claims across all brands. Buying from online third-party marketplaces often voids Jandy and Hayward Expert Line warranties — these products are intended for professional installation. Using non-genuine replacement parts also voids coverage in most cases.
Prevention: Keep Your Heater Running Year-Round
The best ignition lockout is the one that never happens. Most heater failures are preventable with a simple maintenance routine. Here’s the schedule that keeps the lockout codes away.
✅ Heater Maintenance Schedule
-
Weekly: Verify pH and sanitizer levels. Empty pump and skimmer baskets. -
Monthly: Inspect vents and air intakes for bird nests, thick spider webs, and debris. -
Monthly: Clear the burner tray of leaves, acorns, or debris that could cause flame rollout. -
Monthly (off-season): Fire the heater for a few minutes even when not heating — the heat and airflow keeps spiders from nesting in orifices. -
Annually: Professional inspection — gas pressure test, heat exchanger for soot and scale, control calibration. -
Annually: Inspect Thermal Regulator Valve (TRV) for scaling or corrosion. A failing TRV causes internal overheating and a knocking sound. -
Any time: Inspect inside the heater cabinet for evidence of rodent nesting — mice chew wiring harnesses. Use mint sachets or a specialized cover during the off-season.
Use the Fireman’s Switch setting on your automation system (Hayward OmniLogic, Pentair IntelliCenter, or a mechanical timer). This ensures the heater shuts off 20 minutes before the pump stops, dissipating residual heat and preventing internal boiling and scale deposits that restrict tubes.
Red flags that signal bigger problems: Screeching, whistling, or loud banging sounds indicate low flow or internal boiling. Black carbon (soot) on the exterior of the heat exchanger means improper fuel/air mixtures — that’s a job for a technician. Water dripping inside the heater cabinet from pressure switch fittings or header gaskets leads to rusted circuit boards. Don’t ignore these.
ProTuff Pick
Pool Net
Regular skimming keeps leaves and debris out of your pump basket — one of the simplest ways to protect your heater’s water flow. ProTuff’s heavy-duty leaf rake is built to last, backed by the 490 Promise.
ProTuff Pick
Pool Brush Head
Brushing pool walls and floor regularly reduces algae buildup and the organic load on your filter — keeping your filtration running efficiently and your heater’s flow strong. Modular design, magnetic lock, and the 490 Promise.
Water Chemistry That Protects Your Heater
Your heater’s heat exchanger is made of copper alloy — one of the best thermal conductors available, and one of the first things to corrode when water chemistry goes off the rails. Maintaining the Langelier Saturation Index (LSI) between −0.3 and +0.3 is the industry standard for preventing both corrosive etching and mineral scaling.
| Parameter | Ideal Range | What Goes Wrong Outside Range |
|---|---|---|
| pH | 7.4 – 7.6 | Below 7.2: copper erosion. Above 7.8: calcium scaling on heat exchanger tubes. |
| Total Alkalinity | 80 – 120 ppm | Too low: pH swings wildly. Too high: pH locks high, promotes scaling. |
| Calcium Hardness | 200 – 400 ppm | Too low: “aggressive” water strips metal. Too high: calcium deposits in tubes. |
| Salt (if applicable) | 3,200 – 3,400 ppm | Above 5,000 ppm: accelerated heat exchanger corrosion in most models. |
Pro Tip
Improper water chemistry is the single leading cause of denied heater warranty claims. A technician who opens your heat exchanger and finds acid-etched copper will not be able to get you warranty coverage — regardless of how new the unit is. Test weekly during heavy use season.
Salt water does not damage heaters by default — it’s the chemistry that matters, not the salt itself. A properly balanced salt pool with pH in range and calcium hardness maintained will not harm a heater any faster than a traditional chlorine pool.
Do not run an automatic cleaner while the heater is on. Manufacturer documentation advises against this — a clogged cleaner can restrict flow enough to trigger pressure switch lockouts and high limit trips, even on an otherwise well-maintained system.
Frequently Asked Questions
What does “ignition failure” mean on a pool heater?
An ignition failure means the heater attempted to start its burner but did not successfully detect a stable flame within the allowed trial period. The control board then shuts off the gas valve and locks out the ignition system to prevent unburned gas from accumulating in the combustion chamber. It is a safety response, not a mechanical breakdown.
Why does my pool heater keep going into ignition lockout?
Recurring ignition lockouts — where the heater fires fine at first but locks out after a few weeks or seasons — are most commonly caused by spider nests in the burner orifices, a degrading flame sensor that can no longer hold adequate microamp current, or a gas supply pressure issue that looks fine at rest but drops under load. Start with a thorough inspection of the far-left orifice and a multimeter check of the flame sensor current.
Can I clear an ignition lockout myself?
Yes, for most causes. Start by restoring water flow — clean baskets and backwash the filter, then power cycle the heater at the breaker. If the lockout came from low flow, it will clear. For HF (high flame) codes on Hayward, a power cycle at the breaker clears erroneous readings. For internal component failures like a cracked igniter or oxidized flame sensor, those parts can be replaced by a handy homeowner. Gas system issues require a licensed professional.
Can spiders really cause my pool heater to fail?
Yes — and it is one of the most common ignition failure causes on Hayward H-Series heaters specifically. Spiders are attracted to the trace amounts of natural gas odorant and build nests inside burner orifices, especially the far-left orifice on Hayward units. The webbing partially or fully blocks the gas flow to that burner, causing ignition failure or a brief light-then-die sequence. Firing the heater briefly once a month during the off-season is the easiest prevention method.
How much does it cost to fix a pool heater ignition lockout?
It can cost nothing — if the cause is a dirty filter or closed valve, the fix takes 15 minutes and zero dollars. For parts, expect roughly $30–$40 for a flame sensor, $60–$100 for an HSI igniter, and up to $350 for an ignition control module. Professional service calls run $150–$300 for diagnostics and minor repairs. Heat exchanger replacement, the worst-case internal failure, costs $500–$1,500 and often makes a full heater replacement more economical on older units.
Is it safe to bypass a pool heater safety switch to get it running?
No — bypassing a safety switch is never safe. High limit switches, roll-out switches, and pressure switches exist because the heater will destroy itself or create dangerous conditions without them. A bypassed high limit switch can allow the heat exchanger to overheat and fail, create fatal carbon monoxide levels inside the unit, or cause a fire. Always find and fix the root cause triggering the switch rather than eliminating the protection.
Does salt water damage a pool heater?
Not on its own. Salt water pools heat just as reliably as traditional chlorine pools, provided the water chemistry is properly balanced. The damage comes from improper chemistry — low pH, low calcium hardness, or excessive salt levels above 5,000 ppm — not from salt itself. Maintain pH between 7.4 and 7.6 and calcium hardness between 200 and 400 ppm, and your heater will handle a salt water pool without issue.
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Disclaimer: This article is for informational purposes only and does not constitute professional advice. Pool equipment installation and maintenance involve electrical, plumbing, and chemical hazards that can cause serious injury or property damage. Always consult a licensed, qualified professional before performing any work on your pool equipment. ProTuff Products assumes no liability for actions taken based on the information provided in this article. Product specifications, prices, and availability are subject to change and should be verified with the manufacturer.
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