How to Read and Reset Weil-McLain Boiler Error Codes Like a Pro

Hey There from Tony:

Hey hey—Tony here. So your boiler’s flipping out and throwing codes like it’s trying to talk in Morse? Trust me, I’ve been there. Whether it's a blinking LED or a cryptic number on the display, your Weil-McLain boiler is trying to tell you something. And no, it’s not always a death sentence.

This guide is for homeowners who want to take the mystery out of those error codes—and maybe even fix a simple issue without calling in a tech and paying a hundred bucks for a 2-minute reset. Let's break it down, one code at a time. 🔍

 

Step One: Know Your Boiler Type

Weil-McLain makes a wide range of boilers—from older gas-fired units like the CGa Series to newer high-efficiency models like the Evergreen, Ultra, and AquaBalance.

Each model has its own way of communicating errors:

• Classic boilers (CGa, EG, etc.) use blinking LEDs or diagnostic lights

• Modern digital models (Ultra, Evergreen) use alphanumeric codes on an LCD screen

Before we go further, grab your boiler’s installation or service manual (you can also grab them from Weil-McLain’s resource center) to follow along with your model’s exact diagnostics.

 

The Most Common Weil-McLain Boiler Error Codes (And What They Mean)

Here's a breakdown of the most frequent error codes you're likely to see:

 

1. “E02” – Ignition Failure

• What it means: The boiler tried to light but failed.

• Why it happens: No gas flow, dirty flame sensor, or bad ignitor.

• What to do: Check the gas valve is open. Power-cycle the unit. If that doesn’t do it, the ignitor or flame sensor may need cleaning or replacing.

💡 Pro Tip: A light sanding of the flame sensor with emery cloth can sometimes fix this.

 

2. “E04” – Flame Detected When It Shouldn’t Be

• What it means: The boiler thinks there’s a flame before ignition.

• Why it happens: Flame sensor is dirty, or the gas valve is leaking slightly.

• What to do: Shut off gas, clean the flame sensor, and check gas pressure. You’ll need a qualified tech if gas continues to leak.

🔗 Learn more about flame sensor issues in this detailed troubleshooting guide from Cedarwood Heating.

 

3. “E13” or “b26” – Low Water Pressure / Flow Fault

• What it means: Not enough pressure or flow through the system.

• Why it happens: Closed valve, air in the loop, dirty system.

• What to do: Bleed the system, check auto-fill valve and expansion tank. Look at your system pressure—it should be around 12–15 PSI cold.

🛑 Don’t keep resetting if this one comes back—low water can damage the heat exchanger.

 

4. “E27” – Outlet Water Too Hot / Short Cycling

• What it means: The outlet sensor is reading over 200°F.

• Why it happens: Bad sensor, blocked pipes, or poor flow.

• What to do: Check for obstructions, clean the strainer, and test your circulator pump. A failed sensor may need replacing.

👀 You can check if this is legit using an IR thermometer at the outlet pipe.

 

5. Flashing Red LED (Non-Digital Models)

• What it means: Could indicate ignition lockout or limit fault depending on blink pattern.

• Why it happens: Could be a bad rollout switch, overheating, or dirty burner.

• What to do: Count the blinks (1 flash = lockout, 2 flashes = limit trip, etc.) and consult your unit’s blink code chart.

For a solid rundown of blinking boiler diagnostics, visit HeatingHelp’s boiler diagnostics article.

 

How to Safely Reset a Weil-McLain Boiler

Sometimes, a reset clears a temporary fault and gets you back in action. But don’t just mash the button and walk away.

Step-by-Step Reset:

1. Turn off power to the boiler at the service switch or breaker.

2. Wait 30 seconds.

3. Turn the power back on.

4. If your model has a reset button (usually on the control board), press it once.

5. Watch for startup sequence—fan, ignition, flame.

🔧 If it resets and runs: great. If it faults out again within 15 minutes, you’ve got a bigger issue. Don’t keep resetting—it could damage the unit or void the warranty.

Weil-McLain recommends no more than two resets in a row.

 

When to Call a Pro

Now look, I’m all for getting your hands dirty—but there’s a line. If you’ve reset your boiler once or twice and that same code keeps flashing, it’s probably time to stop poking around and call in a licensed pro.

Here are the red flags you don’t ignore:

• You smell gas – Shut everything down immediately and evacuate. This is serious.

• You hear banging, clanging, or hissing – Could be air in the lines, sediment buildup, or worse.

• Pressure keeps climbing above 25 PSI – That’s not just bad—it’s dangerous.

• You see visible leaks around fittings, valves, or the boiler housing.

If any of these show up—or you're simply in over your head—call in a certified technician. The folks over at Angi do a good job outlining exactly when to call a heating repair service, and it’s worth bookmarking for peace of mind.

And hey, if your boiler is older than your teenager, throwing a new code every week, or just costing you way more in repairs than it’s worth, it might be time for an upgrade. You can check out the Weil-McLain collection at The Furnace Outlet for units that are reliable, efficient, and ready to install.

 

Bonus: DIY Boiler Code Log

Print this out and tape it near the boiler. Every time you get a code, write it down:

Knowing the pattern can help your tech diagnose faster and save you money.

 

Goodbye from Tony:

Well look at you—reading boiler codes like a boss. 🔥

Look, I know these things can feel like they’re written in robot-speak, but once you understand the basics, you’ll stop sweating every time a light blinks. Most errors come down to air in the lines, sensors gone wonky, or something simple like a closed valve. But hey—don’t guess. Read the code, check the manual, and reset once. If it still acts up, it’s trying to tell you something.

And remember—if your boiler's older than your favorite hoodie and coughing up more codes than a video game, you might want to scope out a new one. Start with the Weil-McLain collection at The Furnace Outlet. That’s where I’d send my sister.

Need some tune-up tips for your boiler? Visit my guide: Top 10 Signs Your Boiler Needs a Tune-Up (Before Winter Hits).

Stay sharp, stay safe, and never fear the blinking light. Catch you on the next one.
—Tony, the trusted tech 🔧