Hey folks, Mike Sanders here again 👋
If you’ve ever walked past your Weil-McLain boiler and seen a blinking code flashing on the screen, you’re not alone—and no, it doesn’t mean it’s time to panic or rip the whole thing out.
Those error codes are your boiler’s way of telling you what’s wrong—kind of like your car’s check engine light, but way more specific.
In this blog, I’m gonna break down the most common Weil-McLain boiler error codes, what they actually mean, and how to fix ‘em (or when to call in the cavalry 🔧).
We’ll keep it simple, clear, and right to the point—no tech jargon you can’t understand. Let’s decode your boiler, shall we?
What Are Boiler Error Codes, Anyway?
Think of error codes as a boiler’s built-in diagnostic system. Most newer Weil-McLain models like the ECO Tec, Ultra, and AquaBalance have digital control boards that display error codes when something’s out of whack—whether it’s water pressure, ignition, venting, or sensor issues.
You’ll usually see these codes pop up on the boiler’s LCD panel, often with a status light blinking alongside it.
Some codes are no big deal—a quick reset will do the trick. Others? They could be early signs of a serious problem that needs attention before it gets worse (or dangerous).
Let’s walk through the ones I see most often in the field.
Error Code E02 – Ignition Failure
This one’s a classic. Error E02 means your boiler tried to fire up… but no flame was detected.
Possible Causes:
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No gas supply (check shut-off valve or empty propane tank)
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Faulty ignition electrode
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Flame sensor not detecting flame
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Dirty burner or pilot
What You Can Try:
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Make sure your gas is on.
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Reset the boiler and watch it try to ignite.
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Listen for clicking sounds (igniter working) or smell for gas (carefully!).
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Check for blockages or debris in the burner.
When to Call In a Pro:
If you’ve got fuel and still no flame, you might be dealing with a bad flame sensor or ignition control module. These aren’t terribly expensive parts, but you’ll want a tech to handle them safely.
✅ Tip: If you smell gas, shut off the boiler immediately and call your gas company or HVAC tech. Don’t risk it.
More info: Advanced Boilers – Boiler Troubleshooting
Error Code E04 – High Limit Exceeded
When you see E04, your boiler water got too hot—hot enough to trip the high-limit safety shutoff.
Possible Causes:
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Faulty high-limit sensor
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Circulator pump not running (no water movement = heat buildup)
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Air trapped in the system
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Clogged or closed valves
What You Can Try:
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Bleed the radiators to release trapped air.
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Check if the circulator pump is humming (or vibrating) during operation.
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Make sure valves to the radiators or loops are open.
If you ignore this one, you’ll risk boiling water inside the system—and nobody wants a geyser in the basement 🌋.
More help: HVAC School – Circulator Pump Basics
Error Code E10 – Low Water Pressure
This one’s a doozy. E10 means your system’s water pressure is too low to function safely—usually under 12 psi.
Symptoms You’ll See:
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No heat or hot water
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Cold radiators or baseboards
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Gurgling sounds in the system
What You Can Try:
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Look at the boiler’s pressure gauge—anything below 12 psi needs attention.
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Locate the filling loop (usually a silver braided hose under the boiler).
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Slowly open the valves to add water until the gauge reads around 15 psi.
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Close the valves. Always.
🚨 Don’t overfill—it can trip a different error code or mess up your expansion tank.
Still low? You might have a leak or a broken pressure relief valve. This is when it’s smart to call a tech to inspect for hidden damage.
Extra read: Energy.gov Guide to Boilers
Error Code E13 – Flame Signal Lost
This one’s a cousin of E02. It means the burner lit but couldn’t maintain the flame, so it shut down.
Possible Causes:
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Dirty or misaligned flame sensor
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Weak gas flow
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Venting blockage causing incomplete combustion
What You Can Try:
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Remove and clean the flame sensor with fine steel wool (only if you’re comfortable).
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Check for condensation buildup in the flue or vent pipe.
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Make sure there are no birds' nests or ice blocking the intake/exhaust vents (yep, I’ve seen it 🐦❄️).
If it keeps coming back after resets, your gas valve might be to blame—and that’s definitely one for the pros.
Error Code E28 – Condensate Blockage
Condensing boilers like the Weil-McLain ECO Tec remove excess heat by condensing water vapor in the exhaust. That water (called condensate) drains through a trap and out a pipe.
If you see E28, it means that condensate isn’t draining properly.
Likely Culprits:
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Frozen drain line
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Sludge or debris in the trap
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Improper slope of the drain pipe
What You Can Do:
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Remove the trap (after turning off the boiler!) and clean it out.
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Pour a little vinegar through the line to break up gunk.
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Insulate outdoor drain lines in cold weather to prevent freezing.
More tips: Duncan – Frozen Condensate Drain
Boiler Keeps Locking Out? Here's What That Means
Many Weil-McLain boilers will go into lockout mode after repeated ignition failures or major faults. When this happens, the boiler won’t restart until manually reset or serviced.
Lockout indicators include:
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Blinking red lights
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E02/E13 repeated errors
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Control panel displaying “LOCKOUT”
Resetting the Boiler:
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Turn off the boiler using the power switch.
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Wait 30 seconds.
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Turn it back on and watch the ignition cycle.
If it resets and works—great. If not, or if it keeps locking out daily, it’s time for a proper diagnostic by a trained tech.
Pro Tip: Keep a Boiler Log 📘
I always tell homeowners: keep a little notebook near your boiler. Write down error codes, what time they happened, and what you did (reset, added water, etc.). This makes life way easier for your HVAC tech and can even help you spot patterns before something big fails.
When to Call a Pro (and What to Ask)
Sometimes, a reset or pressure top-up will solve the problem. But if any of these keep happening—or if you feel unsure—get a licensed technician involved.
What to ask when you call:
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“Do you have experience with Weil-McLain models?”
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“Can you check my flame sensor and ignition module?”
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“Do you inspect the condensate system and pressure sensors during service?”
Letting them know you’ve already looked up the error codes helps show you’re paying attention—and helps them prep for the job 👍.
Final Thoughts from Mike
Look, error codes might feel intimidating at first. But once you know what they mean, it’s like your boiler is talking to you. And with a solid understanding of the common ones, you’re not just reacting—you’re staying ahead of the game.
Weil-McLain makes solid boilers, but even the best equipment needs attention now and then. Know the codes. Watch for the signs. And when in doubt, bring in the pros.
Got questions? Head over to The Furnace Outlet’s Weil-McLain boiler collection or drop us a message. We're here to help you keep things running hot and smooth 🔥
Need some maintenance tips? Visit my guide: Step-by-Step Guide to Annual Weil-McLain Boiler Maintenance.
Stay safe and stay warm,
—Mike Sanders 🧰💪
