🔧 Introduction: The Day I Replaced My Old Boiler
I’ll never forget the first chilly morning when my old boiler finally gave up. After more than 30 years of faithful service, it sputtered, groaned, and left my house ice cold.
As a homeowner who likes to tackle projects, I wasn’t about to just hand over everything to a contractor without understanding what was involved. So I decided to do what I could myself—and then call in a pro for the parts that required expertise.
In the end, I chose the Weil-McLain CGA-5 Series 3 cast iron boiler. I picked it because of its durability, reliability, and the reputation Weil-McLain has built over decades. But just as important as picking the right unit was making sure it was installed correctly.
This guide walks through everything I learned—step by step—from unpacking the boiler to firing it up for the first time. If you’re planning to replace your own system, or you’re just curious about what’s involved, this guide will give you a clear picture of the process.
📦 Step 1: What Comes in the Box (and What Doesn’t)
When my Weil-McLain boiler arrived, the first thing I did was unbox it. And here’s something every homeowner should know:
The boiler itself is just the beginning.
What’s Included:
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The boiler body (cast iron sections pre-assembled).
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Built-in safety controls (limit switch, pressure relief valve).
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Gas valve assembly.
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Instruction manual and warranty paperwork.
What’s Not Included (You’ll Need to Buy Separately):
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Circulator pump (moves hot water through your system).
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Expansion tank (absorbs pressure changes).
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Venting components (chimney liner or vent pipe).
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Thermostat (if you want an upgrade).
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Zone valves or controllers (if you’re dividing your home into heating zones).
👉 Pro tip: Always check your specific model’s manual before installation. Here’s Weil-McLain’s CGA Series 3 documentation.
🛠️ Step 2: Tools & Prep Work Before Installation
Before doing any real work, I laid out my tools. Here’s what I used:
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Pipe wrenches (large and small).
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Tubing cutter.
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Level.
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Drill with bits.
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Electrical screwdriver set.
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Gas-rated pipe dope and Teflon tape.
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Bucket and hose for draining.
Safety Gear:
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Gloves.
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Goggles.
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Carbon monoxide (CO) detector.
Space Prep:
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Cleared out my utility room.
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Made sure I had the required clearance per code (check your manual—typically 24” front clearance and 6” sides).
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Installed a CO detector nearby for safety.
👉 If you’re not sure about code requirements, see Energy.gov’s boiler installation safety guidelines.
🔥 Step 3: Removing the Old Boiler
This was the part that tested my patience (and my back).
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Drained the system. I connected a hose to the boiler drain and ran it outside.
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Shut off the gas line. Always double-check this before touching anything.
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Disconnected electrical. Marked wires with tape so I knew where they reconnected later.
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Cut and capped water lines.
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Moved the old boiler. Here’s where you really need a helper—the cast iron is heavy.
Pro tip: Don’t try to haul an old boiler out yourself. Rent a dolly or ask a contractor to dispose of it for you.
📏 Step 4: Setting the New Boiler in Place
Once the old unit was gone, it was time to set the new Weil-McLain.
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Used a level to make sure it sat evenly on the basement floor.
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Checked that clearances matched the manual’s requirements.
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Positioned it so the gas valve and water inlets were accessible.
Here’s something I learned: an unlevel boiler can cause air pockets in the water system, which makes circulation noisy and inefficient. Take your time here.
🚰 Step 5: Connecting Gas and Venting (Why Mike Called a Pro)
This is where I drew the line. I’m all about DIY, but I know when to step back.
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Gas line: My pro checked that the pipe size could handle the 133,000 BTU demand. (Undersized gas piping is a common mistake.)
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Venting: Because the CGA-5 is non-condensing, it needed a proper chimney connection with a liner. This keeps exhaust gases moving safely out of the house.
👉 Improper venting is dangerous. For code-approved venting guidance, see HVAC.com’s boiler venting guide.
⚡ Step 6: Wiring and Thermostat Hookup
The electrical side was more straightforward:
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Connected the boiler’s control panel to power.
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Hooked in the thermostat wires (labeled beforehand).
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Added a new smart thermostat for better scheduling and energy use.
👉 If you’re upgrading to a smart thermostat, check compatibility. Here’s ENERGY STAR’s guide to smart thermostats.
💧 Step 7: Filling and Purging the System
After the physical install came the water side:
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Slowly opened the fill valve to add water.
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Watched the pressure gauge until it hit about 12–15 psi (standard cold-fill pressure).
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Bled air from radiators using bleeder valves.
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Re-checked pressure.
Trapped air is the #1 cause of noisy radiators, so don’t skip this step.
👉 For a helpful walkthrough, see Bob Vila’s guide to bleeding radiators.
🔥 Step 8: First Firing & Safety Checks
This was the moment of truth.
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Turned the gas back on.
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Followed the ignition sequence in the Weil-McLain manual.
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Let the system run while checking for:
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Gas leaks (used a soapy water solution).
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Water leaks at joints.
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Proper flue draft (no backdraft into the basement).
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Monitored CO detector.
Everything ran smoothly, and after 20 minutes the radiators started heating up. Success!
🧑🔧 Mike’s Lessons Learned
Here are the big takeaways from my installation:
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Do what you can, but know your limits. Prep work (draining, cleanup, unboxing) is perfect for DIY. Gas line and venting? Call a pro.
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Have extra fittings on hand. Even with planning, I needed extra elbows and adapters.
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Label wires. Saved me a lot of headaches during reconnection.
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Plan for weight. Cast iron boilers are heavy. Don’t risk your back—rent a dolly or hire help.
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Budget for extras. Circulators, expansion tanks, and vent kits add to the total cost.
💡 Conclusion: DIY vs. Pro—Finding the Right Balance
At the end of the day, installing a boiler isn’t like painting a room or swapping out a faucet. It’s a project that combines plumbing, gas work, and electrical—all areas where safety is critical.
If you’re a hands-on homeowner like me, you can definitely take on prep work and even parts of the water system. But for gas and venting, always call a licensed professional.
Choosing a Weil-McLain cast iron boiler made the effort worth it. It gave me a durable, reliable heating system I know will last decades. And now, when I hear it running quietly in the basement, I feel both pride in what I did and confidence in what the pros handled.
In the next topic we will know more about: Maintenance Checklist: Keeping Your Weil-McLain CGA-5 Boiler Running Smooth
