Pool Heater Pilot Won’t Stay Lit: Causes, Fixes, and When to Call a Pro

Gas safety first: If you smell gas, hear hissing, see soot, suspect a cracked heat exchanger, or are uncomfortable working around gas appliances, stop and call a qualified pool heater technician or your gas utility. Do not bypass safety switches, tape down pilot buttons, or modify gas controls.

You head out to warm up the pool for a weekend swim, hit the ignition button, and… nothing. The pilot lights for a second, maybe two, then dies. You try again. Same result. Your pool heater pilot won’t stay lit, and now you’re staring at 68°F water wondering if you’ll ever enjoy a warm swim again.

Good news: this is one of the most common pool heater problems, and about 70% of the time, you can fix it yourself without calling a technician. The culprit is usually something simple — a dirty thermocouple, a clogged pilot tube, or wind sneaking into your heater cabinet. I’ve seen homeowners spend $300 on service calls for problems they could’ve solved with a wire brush and 20 minutes.

Let’s walk through exactly what’s happening inside your heater, why that pilot keeps dying, and how to get it burning steady again.

Understanding Why Your Pilot Light Keeps Going Out

Before you grab any tools, it helps to understand the safety mechanism that’s actually working correctly — even though it’s frustrating you right now.

How the Pilot/Thermocouple System Works

Your pool heater’s pilot light isn’t just a tiny flame sitting there for show. It’s part of a safety system designed to prevent gas from flooding your heater (and your backyard) if ignition fails.

Here’s the chain of events:

1. You press the ignition button, which opens the gas valve manually
2. Gas flows to the pilot assembly and ignites
3. The flame heats a sensor called a thermocouple
4. The thermocouple generates a small electrical current (about 25-30 millivolts)
5. That current tells the gas valve “hey, there’s a flame here, keep gas flowing”
6. You release the button, and the valve stays open because the thermocouple is sending its signal

When your pilot won’t stay lit, one of these steps is failing. Either the thermocouple isn’t heating up properly, it’s not generating enough voltage, or the gas valve isn’t receiving the signal.

Think of it like a deadman’s switch on a lawnmower. The moment that switch doesn’t sense pressure from your hand, the engine cuts. Your thermocouple works the same way — no flame detection, no gas.

The 5 Most Common Causes

Based on what I’ve seen across Hayward, Pentair, Raypak, and Jandy heaters, here’s what’s usually wrong:

1. Dirty or corroded thermocouple (45% of cases)
2. Clogged pilot orifice or tube (25% of cases)
3. Wind or draft interference (15% of cases)
4. Faulty thermocouple requiring replacement (10% of cases)
5. Gas pressure issues (5% of cases)

Notice that the most common problems are also the cheapest to fix. Let’s tackle them in order.

Diagnosing the Problem: Where to Start

Don’t start replacing parts randomly. Spend 5 minutes diagnosing first, and you’ll save yourself time and money.

Check #1: How Long Does the Pilot Stay Lit?

Time it with your phone. This tells you a lot:

• Pilot dies immediately when you release the button (0-3 seconds): Thermocouple isn’t heating up at all, or it’s completely failed
• Pilot dies after 5-10 seconds: Thermocouple is partially working but not generating enough millivolts
• Pilot dies after 20-30 seconds: Weak thermocouple signal, borderline gas valve, or intermittent wind interference
• Pilot stays lit but main burner won’t ignite: Different problem — likely a high-limit switch or control board issue

Check #2: What Does the Flame Look Like?

When you’re holding the ignition button, look at the pilot flame (carefully — don’t stick your face in there).

• Strong blue flame with yellow tip, engulfing the thermocouple: Good. The thermocouple should be getting plenty of heat.
• Weak, lazy blue flame that barely touches the thermocouple: Not enough heat reaching the sensor. Probably a clogged pilot orifice.
• Yellow or orange flame: Incomplete combustion, possible airflow issue or dirty burner.
• Flame that flickers or gets blown sideways: Wind interference.

Check #3: Inspect the Thermocouple Visually

Open your heater cabinet and locate the pilot assembly. The thermocouple is a thin copper tube (about 1/8″ diameter) with a metal probe tip positioned directly in the pilot flame path.

Look for:
– White, gray, or green corrosion on the probe tip
– Black soot buildup covering the probe
– Bent or damaged thermocouple positioning (tip should be in the hottest part of the flame)
– Loose connection where the thermocouple attaches to the gas valve

Fixing a Dirty Thermocouple (Most Common Solution)

If your thermocouple looks even slightly dirty, start here. This fix takes about 10 minutes and costs nothing if you already have basic supplies.

What You’ll Need

• Fine-grit sandpaper (220-grit works great) or emery cloth
• Clean rag
• Wrench set (usually 7/16″ or 3/8″ for the thermocouple fitting)
• Compressed air can (optional but helpful)

A basic sandpaper assortment pack will handle this job and dozens of other home projects.

Step-by-Step Cleaning Process

Step 1: Turn off gas supply to the heater. There’s usually a shutoff valve on the gas line within a few feet of the heater. Turn it perpendicular to the pipe.

Step 2: Wait 5 minutes for any residual gas to dissipate. Don’t skip this.

Step 3: Use your wrench to loosen the thermocouple fitting where it connects to the gas control valve. This is usually a brass nut. Turn counterclockwise. You don’t need to remove it completely — just loose enough to pull the thermocouple probe back from the pilot assembly.

Step 4: Gently sand the thermocouple probe tip. Use light pressure and work around the entire surface. You’re removing oxidation and carbon buildup that acts as an insulator, preventing the flame’s heat from reaching the actual sensor inside.

Step 5: Wipe the probe with your clean rag. Blow out any dust with compressed air if you have it.

Step 6: While you’re in there, sand the threads of the fitting too. Corrosion here can cause a poor electrical connection.

Step 7: Reinstall the thermocouple. Make sure the probe tip is positioned directly in the pilot flame path — usually about 1/2″ into where the flame burns. Tighten the fitting snugly, but don’t gorilla it. Over-tightening can damage the seal.

Step 8: Turn the gas back on. Wait 2 minutes, then try lighting the pilot again. Hold the ignition button for a full 60 seconds before releasing.

For about 45% of people reading this, the problem is now solved. If the pilot still dies, move on to the next fix.

Clearing a Clogged Pilot Orifice

The pilot orifice is a tiny hole (often just 0.5mm to 1mm diameter) where gas exits to feed the pilot flame. Spiders love building webs in here. Dust accumulates. And after a few seasons, that pinhole gets partially blocked.

Signs of a Clogged Pilot Orifice

• Weak, small pilot flame
• Flame that’s more orange than blue
• Hissing sound when pilot is lit (gas struggling to escape)
• Pilot takes forever to light

How to Clean It

Step 1: Turn off gas and wait 5 minutes.

Step 2: Locate the pilot assembly. You may need to remove a small bracket or clip holding it in place.

Step 3: Find the pilot orifice. It’s the small brass fitting where gas enters the pilot tube. Some heaters have removable orifices; others have a fixed orifice built into the pilot assembly.

Step 4: For removable orifices: Unscrew it carefully. Use compressed air to blow through it (from the outlet side back toward the inlet). Never use a wire or needle — you can enlarge the orifice and permanently affect flame size.

Step 5: For fixed orifices: Use a can of compressed air to blow into the pilot tube. Work from multiple angles.

Step 6: While you’re there, blow out the entire pilot tube assembly. Spider webs and dead insects are common finds.

Step 7: Reassemble and test.

A can of electronics-grade compressed air is perfect for this — it’s residue-free and has enough pressure to clear debris without damaging components.

Dealing with Wind Interference

Pool heaters sit outside, exposed to whatever weather your backyard throws at them. And even though they have cabinets, wind can sneak in through vents and blow out pilot lights — especially on gusty days.

Quick Tests for Wind Problems

• Does the pilot stay lit on calm days but die when it’s breezy?
• Can you hear wind whistling inside the heater cabinet when the pilot goes out?
• Does the flame flicker erratically before dying?

If yes, wind is likely your issue.

Solutions for Wind Interference

Adjust louvers or vents: Some heaters have adjustable air intake louvers. Try partially closing them on the windward side.

Check cabinet seals: Inspect the door gasket and any panel seams. Replace worn gaskets.

Add wind shielding: If your heater is in a particularly exposed location, consider adding a wind screen. Don’t block airflow completely (the heater needs combustion air), but strategically placed barriers can redirect gusts.

Relocate the heater: This is a last resort, obviously. But if you installed the heater in a wind tunnel location, it might be worth the expense long-term.

When to Replace the Thermocouple

If cleaning didn’t work and you’ve ruled out pilot tube clogs and wind, the thermocouple itself may be worn out. They’re not designed to last forever — most manufacturers rate them for 4-7 years of regular use.

Testing with a Multimeter

Want to know for sure? You can test thermocouple output:

1. Light the pilot and hold it lit
2. Set your multimeter to DC millivolts
3. Connect one probe to the thermocouple tip (if accessible) and one to the connector
4. A healthy thermocouple produces 25-35 millivolts when heated
5. Below 20 millivolts? Replace it.

Buying the Right Replacement

Thermocouples are specific to your heater model. Don’t grab a universal one and hope for the best — lead length, connection type, and probe shape matter.

Find your heater’s model number (usually on a label inside the cabinet) and order the exact OEM part, or a direct replacement. Common brands like Honeywell make cross-compatible thermocouples, but verify compatibility first.

Expect to pay $15-40 for a quality replacement thermocouple. Universal replacement kits work for many standard heaters if you confirm the length and connection style match.

Replacement Steps

1. Turn off gas supply
2. Disconnect the old thermocouple from the gas valve (counterclockwise)
3. Remove the thermocouple from the pilot assembly bracket
4. Install the new thermocouple in the bracket, ensuring the probe tip sits in the pilot flame path
5. Connect to the gas valve and tighten (hand-tight plus 1/4 turn with a wrench)
6. Turn gas on, wait 2 minutes, then test

Gas Pressure Issues (The Less Common Culprit)

If everything above fails, you might have a gas supply problem. This is less common but worth mentioning.

Signs of Low Gas Pressure

• All gas appliances in your home seem to have weak flames
• Pilot flame is steady but tiny, even with clean components
• Heater worked fine until a cold snap (high demand on gas system)

What You Can Do

Check your other gas appliances. Is your water heater’s pilot also weak? Stove burners lower than usual? If yes, call your gas utility — there may be a supply issue on their end, or your regulator may be failing.

For propane users: Check your tank level. Below 20%? The pressure drops significantly. Get a refill.

Beyond these basic checks, gas pressure diagnosis requires tools and expertise most homeowners don’t have. This is when calling a pro makes sense.

When to Call a Professional

You’ve cleaned the thermocouple, cleared the pilot tube, ruled out wind, replaced the thermocouple, and the pilot still won’t stay lit. Now what?

Time to call in backup. Here’s what might be wrong:

• Faulty gas control valve: The valve itself has an internal issue. Replacement runs $150-400 for parts plus labor.
• Control board problems (on electronic ignition heaters): Newer heaters use electronic ignition systems instead of standing pilots. If yours has a control board, it might be the issue.
• Heat exchanger cracks causing backpressure: A damaged heat exchanger can create pressure changes that extinguish the pilot. This is expensive to fix and may mean heater replacement.

A qualified pool heater technician can diagnose these problems with proper equipment. Expect to pay $75-150 for a service call.

Preventing Future Pilot Problems

Once your pilot is burning steady again, keep it that way:

• Annual maintenance: Have your heater inspected and cleaned once per year, ideally before heating season
• Keep the area clean: Debris, leaves, and spiders are your heater cabinet’s enemies
• Cover during off-season: If you close your pool for winter, cover the heater to keep out pests and moisture
• Run the heater monthly: Even in summer when you don’t need heat, fire it up once a month. This prevents rust and keeps components moving.

FAQ

How long should I hold the pilot button before releasing?

Hold it for 30-60 seconds. The thermocouple needs time to heat up and start generating voltage. Releasing too soon is a common mistake — people hold it for 10 seconds, release, and blame the equipment when the pilot dies.

Can I convert my standing pilot heater to electronic ignition?

Not easily. The two systems use completely different gas valves and controls. In most cases, you’d be better off replacing the entire heater if you want electronic ignition. That said, standing pilot heaters are reliable and don’t require electricity to operate — which is actually an advantage during power outages.

Why does my pilot only go out at night?

Temperature. As night falls and the air cools, thermal air currents change. This can create drafts that weren’t present during the day. Wind patterns also shift as the ground and surrounding surfaces cool. Try adjusting cabinet vents or adding wind shielding on the side facing your typical night breeze.

Is it safe to use my pool heater if the pilot keeps going out?

Yes, the safety system is actually working correctly. When the pilot goes out, the thermocouple stops generating voltage, and the gas valve closes. Gas isn’t flooding your heater. The problem is annoying, not dangerous. But fix it anyway — repeatedly trying to light a pilot that won’t stay lit can eventually damage components.

How much does professional pool heater repair typically cost?

Service calls average $75-150 just to show up. Thermocouple replacement by a pro runs $125-200 total. Gas valve replacement is $250-500. Control board replacement is $300-600. Full heater replacement is $2,500-5,000 installed. Before calling a pro, try the DIY fixes in this guide — you might save yourself several hundred dollars.

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Get Your Pool Chemistry Right Too

A working heater is just one part of enjoying your pool. If you’re spending time maintaining your equipment, you should also make sure your water chemistry is dialed in.

Use Pool Chemical Calculator to calculate exactly how much chlorine, pH adjuster, alkalinity increaser, calcium hardness increaser, stabilizer, salt, or other chemicals your pool needs based on your test results. No guessing, no overdosing, no wasted chemicals. Just clear, balanced water ready for your now-heated pool.

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