Gas Pool Heater Won't Ignite — Pilot or Ignition Board Fault
A gas pool heater that attempts to start — you hear the fan come on, a click or two from the igniter — but never produces a sustained flame, points to one of four root causes: no gas supply, a failed igniter or pilot assembly, a faulty gas valve, or a control board that's not sending the correct ignition sequence. This guide walks through the diagnostic sequence a pool technician uses, starting with the cheapest and most likely causes.
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Common Symptoms
- Heater display shows 'ignition failure' or blinks an error sequence
- Fan activates but no ignition click heard from the igniter
- Igniter clicks but gas doesn't light (no flame sensor confirmation)
- Flame lights momentarily then extinguishes within 4 seconds
- Heater attempts 2–3 ignition trials then locks out
- Unit smells of gas briefly but won't sustain combustion
Most Likely Causes
- 1
Failed Hot Surface Igniter or Spark Igniter
Hayward H-Series and older models use a spark igniter. Pentair MasterTemp uses a hot surface igniter (silicon carbide or silicon nitride). Igniters crack with age — a cracked SiC igniter glows dimly or not at all. A spark igniter with a cracked electrode tip won't generate a sufficient arc.
- 2
Gas Supply Issue
Insufficient gas pressure (below 4" WC for natural gas, 11" WC for propane) prevents the burner from lighting. Check that the gas service valve is fully open, the gas meter is not in bypass mode, and the supply pressure is adequate with a manometer.
- 3
Faulty Flame Sensor (Rectification Rod)
After ignition, the flame sensor confirms the burner is lit by passing a small DC current through the flame. A contaminated or oxidized flame sensor sends a weak signal — the control board interprets this as 'no flame' and shuts the gas valve, causing the infamous light-then-extinguish cycle.
- 4
Failed Gas Valve
The combination gas valve controls main burner gas flow. If the valve solenoids have failed or the operator's coil has shorted, the gas valve won't open on command. Test by verifying 24V is reaching the valve during the trial period.
- 5
Control Board or Ignition Module Failure
The control board sequences the ignition cycle: open gas valve → spark/heat igniter → confirm flame → run burner. A failed board may skip steps, not produce the 24V signal to the gas valve, or fail to read the flame sensor input.
- 6
Dirty or Blocked Burner Tray
A corroded burner tray with clogged burner ports produces a weak, patchy flame that the flame sensor can't confirm. Spider webs, debris, and copper oxide (green deposits) on burner orifices are common in units that sit idle over winter.
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Quick DIY Checks
If you smell gas and cannot identify the source, leave the area and call your gas utility. Do not operate any electrical switches. Do not attempt ignition until the leak is located and repaired.
Always turn off the heater's dedicated gas valve and disconnect power before working inside the heater cabinet. Allow the burner to cool for at least 15 minutes before handling burner components.
- 1Verify gas supply: confirm the main gas valve to the heater is fully open (handle parallel to pipe). Check that other gas appliances in the home are operating normally — if they're also out, the issue is with gas supply or the meter.
- 2Remove the heater front panel and locate the igniter. On Pentair MasterTemp, the hot surface igniter is at the front of the burner tray. Inspect for visible cracks. For SiC igniters, test resistance with a multimeter — should read 40–90 ohms. An open circuit means it's failed.
- 3Locate the flame sensor rod (a single metal rod angled into the burner flame path). Using fine steel wool or emery cloth, lightly clean the tip of the sensor rod to remove oxide buildup. Do not use sandpaper — it leaves abrasive particles.
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Try Pro — $7.99/mo- 4During a test ignition cycle, measure 24V AC at the gas valve terminals with a multimeter. If voltage is present but the valve doesn't open, the valve solenoid has failed. If no voltage is present, the board is not sending the signal.
- 5Inspect the burner tray for corrosion, clogged orifices, and debris. Remove the burner tray and clean with compressed air. Look inside each burner port — use a wire brush to clear blocked ports.
- 6Reset the heater by turning it off, waiting 30 seconds, then turning it back on. Some Hayward and Pentair models require a manual reset after repeated ignition lockouts. Consult the display for error code sequences.
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Repair vs Replace
Ignition components (igniter, flame sensor) are cheap and straightforward to replace. Even a gas valve replacement ($80–$150 in parts) is cost-effective if the heater is under 10 years old. Control board replacement at $300–$500 starts to push the economics toward a new unit for heaters over 12 years old.
Est. Repair Cost
$30–$150 (igniter, flame sensor, or gas valve)
Est. Replacement Cost
$2,000–$4,500 for a new pool heater installed
Recommended Tools & Parts
- Buy on Amazon →
Pentair MasterTemp Hot Surface Igniter
Replacement silicon nitride igniter for Pentair MasterTemp and Max-E-Therm heaters. Part 42001-0052S. Improved SiN design lasts longer than original SiC.
$35–$70
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Hayward H-Series Igniter/Flame Sensor
Spark igniter and flame sensor assembly for Hayward H-Series pool heaters. Check model number (H150, H200, H250, H300, H400) before ordering.
$40–$80
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Pool Heater Gas Valve
Combination gas valve for natural gas or LP pool heaters. Verify inlet/outlet size and BTU rating match your heater's nameplate.
$80–$200
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Pool Heater Control Board
Replacement ignition control board for Hayward or Pentair heaters. Model-specific — confirm part number from your heater's wiring diagram label.
$150–$350
Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.
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Frequently Asked Questions
- My pool heater clicks twice then stops — is that the igniter failing?
- Two clicks then silence usually means the igniter is firing but gas isn't reaching the burner, or the gas is lighting but the flame sensor isn't confirming the flame. Check that the gas valve terminals have 24V during the trial period. Then clean the flame sensor rod. If gas does ignite but the burner shuts off within 2–4 seconds, a dirty flame sensor is almost certainly the cause.
- How often should I replace the pool heater igniter?
- Hot surface igniters (SiC/SiN) typically last 4–7 years with seasonal use. If your heater is having intermittent ignition issues (starts sometimes, fails other times), the igniter is weakening. Proactive replacement costs $35–$70 and prevents a no-heat situation mid-season.
- Can low pool water pressure cause ignition failure?
- Yes. Most gas pool heaters have a pressure switch or flow switch that prevents ignition unless water is flowing through the heat exchanger. If your pool pump isn't priming properly or filter pressure is too high, water flow through the heater may be insufficient to close the pressure switch — so the heater will never reach the ignition sequence. Always verify the pump is running and has adequate flow before diagnosing the heater ignition system.