Pool Heater Won't Ignite: Common Causes

A pool heater that won’t ignite is one of the most frustrating equipment failures — you can hear the controller click, see the LED light, but no flame. Here’s the diagnostic flow that fixes 90% of ignition failures without a service call.

What “won’t ignite” sounds like

• You hear the combustion blower start.
• Maybe you hear a click or two from the gas valve.
• No woosh of ignition.
• The controller shows an “IF” (Ignition Failure) or “IO” (Ignition Lockout) error after 30–60 seconds.

The five most common causes

1. Gas supply problem (most common)

• Propane: tank empty or shut off; check tank level and that the dome valve is open.
• Natural gas: manual shutoff at the heater inlet is closed; check the valve.
• Both: low gas pressure from too-small supply line. Listen for gas at the heater inlet.

2. Dirty flame sensor

The flame sensor is a small metal probe near the burner. Over time it gets coated with combustion residue and can’t detect the flame. The heater interprets “no flame detected” and shuts off the gas after 5 seconds. Pull the sensor, gently sand it clean with fine sandpaper, reinstall.

3. Bad igniter (HSI or spark)

Hot-surface igniters glow bright orange before ignition. Spark igniters click and create visible spark. If you see no glow or hear no spark, the igniter is dead. Replace.

4. Blocked exhaust or air intake

If the pressure switch sees blocked flue, it won’t allow ignition. Birds nesting in flues are surprisingly common. Check for visible obstructions at the top of the flue.

5. Failed gas valve

If everything else checks out (sensor clean, igniter glowing, gas supply confirmed), the gas valve solenoid may have failed. This is a service-tech call — gas valve work requires proper testing.

Heater parts at PST

For full error-code troubleshooting on Hayward Universal H-Series heaters, see our error code guide.