Table of Contents
Introduction
Nothing’s more frustrating than wanting to swim in your heated pool, only to find your heater won’t fire up. You flip the switch, hear some sounds, maybe see lights blinking, but no heat. This problem hits thousands of pool owners every swimming season, and the good news is that most ignition problems have simple causes and solutions.
Pool heaters that won’t ignite usually have problems with one of five main systems: the igniter itself, gas supply, electrical controls, water flow, or safety switches. The igniter burns out most often – it’s basically a wear item that needs replacement every 3-5 years. But gas supply issues, dirty sensors, and airflow problems can also prevent ignition.
Modern gas pool heaters have multiple safety systems that must all work perfectly before ignition occurs. If any single component fails or sends the wrong signal, the heater won’t light. This safety-first design prevents dangerous situations but can make troubleshooting feel like solving a puzzle with missing pieces.
This guide walks you through the most common reasons pool heaters won’t ignite, from simple fixes you can try yourself to problems requiring professional help. We’ll explain how each system works, what goes wrong, and how to identify the actual problem instead of just replacing random parts.
What Would Cause a Pool Heater to Not Ignite?
A pool heater won’t ignite when any part of the ignition sequence fails, but the most common causes are a burned-out igniter (40% of cases), gas supply problems (25%), dirty or faulty sensors (15%), airflow issues (10%), and electrical control failures (10%). Modern gas heaters require all safety systems to function perfectly before allowing ignition.
Common Ignition Failure Causes by Frequency
| Problem |
Frequency |
Primary Symptoms |
Typical Cost to Fix |
| Burned-out igniter |
40% |
No glow, attempts ignition but no flame |
$200-400 |
| Gas supply issues |
25% |
No gas flow sounds, other appliances affected |
$0-650 |
| Dirty/faulty sensors |
15% |
Lights briefly then shuts off |
$150-350 |
| Airflow problems |
10% |
Fan issues, error codes |
$200-500 |
| Electrical failures |
10% |
No activity, error codes |
$300-700 |
The Ignition Sequence Explained
| Step |
What Happens |
Safety Check |
Common Failure Point |
| 1. Call for Heat |
Thermostat signals need for heat |
Temperature verification |
Thermostat failure |
| 2. Flow Check |
System verifies water flow |
Flow/pressure switch |
Dirty filter, closed valve |
| 3. Air Check |
Fan starts, airflow verified |
Pressure switch |
Blocked vents |
| 4. Igniter Heating |
Igniter heats to 2000°F+ |
Temperature sensor |
Burned-out igniter |
| 5. Gas Release |
Gas valve opens |
Multiple safety checks |
Gas valve failure |
| 6. Ignition |
Gas ignites from hot surface |
Flame sensor |
Low gas pressure |
| 7. Flame Proof |
Flame sensor confirms combustion |
Continuous monitoring |
Dirty flame sensor |
Age-Related Failure Patterns
| Heater Age |
Most Common Problems |
Repair vs Replace |
| 0-3 years |
Installation issues, electrical problems, warranty defects |
Always repair (warranty) |
| 3-8 years |
Igniter failure, sensor problems, minor component wear |
Usually repair |
| 8+ years |
Multiple failures, gas valve issues, control board problems |
Evaluate case-by-case |
Hot Surface Igniter Problems
Hot surface igniters are the most common failure point in pool heater ignition systems. These ceramic elements heat to over 2,000°F to ignite gas, but they’re fragile and burn out every 3-5 years with normal use. A failed igniter is the single most likely reason your pool heater won’t light.
Igniter Failure Diagnosis
| Symptom |
What It Means |
Action Required |
| No glow at all |
Complete igniter failure or electrical issue |
Check connections, likely needs replacement |
| Weak orange glow |
Igniter wearing out |
Replace soon |
| Takes >60 seconds to glow |
Failing igniter or voltage issue |
Test voltage, plan replacement |
| Glows but no ignition |
Gas supply or pressure problem |
Check gas system |
| Visible cracks |
Physical damage |
Replace immediately |
Igniter Lifespan Factors
| Factor |
Impact on Lifespan |
Prevention |
| Cycling frequency |
More cycles = shorter life |
Use pool cover, set reasonable temps |
| Power quality |
Voltage fluctuations cause premature failure |
Install surge protector |
| Chemical exposure |
Corrosion weakens element |
Proper ventilation |
| Vibration |
Cracks ceramic element |
Secure mounting, isolate from pump vibration |
| Moisture |
Causes electrical issues |
Keep heater area dry |
Gas Supply Issues
Gas supply problems are the second most common reason pool heaters won’t ignite. These issues range from simple problems like closed valves to complex issues like regulator failure or undersized gas lines.
Gas Supply Troubleshooting Checklist
| Check Point |
What to Look For |
Common Issues |
DIY Fix? |
| Manual valve |
Handle parallel to pipe |
Accidentally closed |
Yes – open valve |
| Gas meter |
Dial movement when heater calls |
No gas service |
No – call utility |
| Other appliances |
Working normally? |
Supply interruption |
No – call utility |
| Propane tank |
Gauge >25% |
Empty tank |
Yes – refill |
| Gas smell |
Any odor detected |
Leak |
No – evacuate, call 911 |
| Line size |
Adequate for BTU rating |
Undersized |
No – professional required |
Airflow and Venting Problems
Common Airflow Issues and Solutions
| Problem |
Location |
Symptoms |
Solution |
| Blocked intakes |
Bottom/sides of heater |
Fan runs but no ignition |
Clear debris, trim vegetation |
| Blocked exhaust |
Top vent |
Error codes, won’t start |
Clear obstruction |
| Damaged venting |
Vent pipes |
CO detector alarms |
Professional repair |
| Fan failure |
Internal |
No fan sound |
Motor replacement |
| Pressure switch |
Internal |
Fan runs, no ignition |
Clean or replace switch |
Electrical Control Issues
Electrical System Diagnostic Guide
| Component |
Test Method |
Good Reading |
Bad Reading |
| Main power |
Check display/lights |
LEDs lit |
No lights |
| Breaker/GFCI |
Visual inspection |
Set, not tripped |
Tripped position |
| Thermostat |
Temperature setting |
Above pool temp |
Below pool temp |
| Control board |
Error codes |
Normal display |
Error codes shown |
| Wire connections |
Visual inspection |
Clean, tight |
Corroded, loose |
Common Error Codes
| Code Type |
Typical Meaning |
Common Cause |
First Action |
| IGN/IGS |
Ignition failure |
Bad igniter |
Check igniter glow |
| FLO/FLS |
Flow issue |
Dirty filter |
Clean filter |
| PRS/PS |
Pressure switch |
Airflow blocked |
Check vents |
| FLM/FS |
Flame sensing |
Dirty sensor |
Clean flame sensor |
| HLS/HI |
High limit |
Overheating |
Check water flow |
Water Flow Requirements
Water Flow Troubleshooting
| Issue |
Symptoms |
Check Points |
Solution |
| Low flow |
Flow error, overheating |
Filter pressure gauge |
Clean/backwash filter |
| No flow |
Immediate shutdown |
Pump operation |
Prime pump, check valves |
| Air in system |
Intermittent operation |
Return jets bubbling |
Purge air, check seals |
| Closed valve |
No flow to heater |
All manual valves |
Open valves fully |
| Flow switch stuck |
False flow errors |
Switch paddle movement |
Clean or replace switch |
Safety Switch and Sensor Problems
Safety System Components
| Component |
Function |
Failure Mode |
DIY Service? |
| Flame sensor |
Detects combustion |
Gets dirty/corroded |
Yes – clean carefully |
| High limit switch |
Prevents overheating |
Trips, needs reset |
Yes – reset button |
| Pressure switch |
Verifies airflow |
Sticks open/closed |
No – replacement needed |
| Flow switch |
Confirms water flow |
Paddle sticks |
Sometimes – check paddle |
| Rollout switch |
Detects flame rollout |
Trips from backdraft |
Yes – reset if safe |
Step-by-Step Troubleshooting Guide
Systematic Troubleshooting Process
| Step |
Action |
What to Check |
If Failed, Then… |
| 1 |
Verify basics |
Power on, thermostat set high, pump running |
Fix basic issues first |
| 2 |
Check displays |
Error codes, LED indicators |
Note codes for diagnosis |
| 3 |
Test safety systems |
Reset switches, check sensors |
Clean sensors, reset switches |
| 4 |
Observe ignition |
Watch igniter, listen for gas |
Identify failure point |
| 5 |
Document findings |
Record all observations |
Prepare for service call |
Ignition Sequence Observations
| What You Observe |
What It Indicates |
Most Likely Problem |
| Nothing happens |
No power or control issue |
Electrical problem |
| Fan runs, no igniter glow |
Igniter circuit failure |
Bad igniter or control board |
| Igniter glows, no gas |
Gas system issue |
Closed valve or gas pressure |
| Brief flame then shutdown |
Flame sensing failure |
Dirty flame sensor |
| Repeated attempts |
Marginal component |
Weak igniter or low gas |
When to Call a Professional
DIY vs Professional Decision Guide
| Situation |
DIY Appropriate? |
Professional Required? |
Reason |
| Gas smell |
Never |
Immediately |
Safety hazard |
| Electrical sparking |
Never |
Immediately |
Fire/shock risk |
| Dirty flame sensor |
Yes (carefully) |
If unsure |
Simple cleaning |
| Tripped breaker |
Yes (once) |
If trips again |
May indicate problem |
| Error codes |
Document only |
For repair |
Diagnosis needed |
| Igniter replacement |
No |
Yes |
Gas safety |
| Control board |
Never |
Always |
Complex diagnosis |
Prevention and Maintenance Tips
Maintenance Schedule for Ignition System
| Frequency |
Task |
Purpose |
DIY/Pro |
| Monthly |
Visual inspection, clear debris |
Prevent blockages |
DIY |
| Quarterly |
Check/clean filters |
Ensure water flow |
DIY |
| Annually |
Professional service |
Complete inspection |
Pro |
| Every 2 years |
Flame sensor cleaning |
Prevent false shutdowns |
Pro |
| Every 3-5 years |
Igniter inspection/replacement |
Prevent failure |
Pro |
Simple DIY Fixes vs Professional Repairs
Repair Classification Guide
| Repair Type |
DIY Skill Level |
Tools Required |
Risk Level |
| Safe DIY Tasks |
Beginner |
Basic hand tools |
Low |
| • Clear debris |
None |
None |
None |
| • Reset breakers |
Basic |
None |
Low |
| • Check thermostat |
Basic |
None |
None |
| Caution DIY Tasks |
Intermediate |
Basic tools |
Moderate |
| • Clean flame sensor |
Moderate |
Steel wool |
Gas/electric hazard |
| • Reset safety switches |
Basic |
None |
May mask problem |
| Professional Only |
Licensed required |
Specialized |
High |
| • Gas work |
Licensed |
Gas tools |
Explosion/CO risk |
| • Electrical diagnosis |
Licensed |
Meters |
Electrocution |
| • Component replacement |
Certified |
Various |
Multiple hazards |
For more information about pool heater maintenance and troubleshooting, consult the Department of Energy’s pool heating resources. Professional service providers can be found through the Pool & Hot Tub Alliance directory.
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