Boiler Not Heating? Here’s the Full Troubleshooting Checklist

Hey—it’s Cold in Here. What Gives? 🥶

Yo, Jake here.
So your boiler’s not kicking out heat, and your house feels more like an icebox than a cozy castle. First off—breathe. This happens, and most of the time, it’s totally fixable without calling in a $200-an-hour tech. 💸

In this no-BS checklist, I’m going to walk you through everything I check when a hot water boiler isn’t heating right. Whether you’ve got a Weil-McLain beast, a combi setup, or a cast iron workhorse, this guide applies to 95% of what you’ll run into.

Grab a flashlight, maybe a wrench, and let’s get to work. 👇

 

Step 1: Is the Thermostat the Culprit?

Before you start tearing into the boiler, make sure the thermostat isn’t the root of the issue. It happens way more often than you’d think.

• Is it set to "HEAT"? (You’d be surprised…)

• Battery dead? Swap 'em.

• Wiring loose or corroded? Pull the cover and check.

• Try jumping the terminals (R and W) to see if the boiler kicks on.

If it’s a smart thermostat, check your app settings or recent updates. Also, make sure it’s connected to Wi-Fi or hasn’t reset itself to some wacky schedule.

Still stuck? This thermostat troubleshooting guide from Asurion is a solid backup.

 

Step 2: Is the Boiler Getting Power? 🔌

Check the obvious:

• Is the boiler switch on (usually near the unit)?

• Check the circuit breaker—if it’s tripped, reset it.

• Blown fuse in the boiler panel? Swap it.

Use a multimeter to test voltage at the terminals if you’re comfortable. No power = no heat. Period.

 

Step 3: Water Pressure Too Low?

Most hot water boilers need about 12–15 psi to operate correctly. Anything lower and the system might not circulate water properly, which means no heat.

Look at the pressure gauge on the side of your boiler. If it’s under 10 psi:

• Check if the fill valve is open

• Make sure your expansion tank isn’t waterlogged

• Add water to the system slowly if needed

Here’s a great step-by-step on refilling boiler pressure from British Gas.

 

Step 4: Check for Air in the System 🫧

Air bubbles in the pipes can block water flow, causing certain zones—or the whole house—to go cold.

Do this:

• Bleed the radiators one by one

• Listen for gurgling or sloshing sounds

• Check for uneven heating room-to-room

A good video walk-through on this comes from Silverline Tools. Super helpful if you're a visual learner like me.

 

Step 5: Circulator Pump Not Running?

This one’s a biggie. The circulator pump moves hot water from the boiler through your system. If it’s busted or stuck, you’ll hear the boiler fire up, but no warmth comes through the pipes.

What to check:

• Feel the pump housing. Is it vibrating or warm?

• Check the zone valves—make sure they’re opening.

• Listen for humming (that’s a good sign—it’s trying to work).

• No movement? You may need to replace the pump. Don’t panic—HeatingHelp.com has a great pump replacement guide.

Tip: If you’ve got a smart zone control board, check the LEDs—one might be blinking a code.

 

Step 6: Pilot Light or Ignition Failure 🔥

Gas boiler? You need a flame.

Older models use a standing pilot light, while newer condensing models have electronic ignition.

Do this:

• If you’ve got a pilot, make sure it’s lit.

  • If it’s out, follow the relighting instructions on the boiler label.

• If it's electronic ignition, listen for clicking or a spark.

  • If nothing happens, check the flame sensor—it might just need a clean.

  • Still nothing? Could be the igniter or control board.

This guide from Ranshaw explains how pilot systems work and how to relight them safely.

 

Step 7: Frozen Condensate Line (For High-Efficiency Boilers) ❄️

If it’s really cold out, the condensate drain line can freeze, which shuts down the boiler. This is common with high-efficiency Weil-McLain units like the Ultra or Evergreen series.

Signs:

• Error code on the display

• Gurgling sounds

• Water pooling near the drain line

Fix it:

• Carefully thaw the line with warm towels or a hair dryer (never a torch)

• Add pipe insulation or heat tape to prevent future freezing

• Check out this forum from Home Improvement

 

Step 8: Boiler Making Weird Noises?

Boilers shouldn’t sound like they’re haunted. If you hear:

• Banging or clunking: Could be kettling (scale buildup)

• Whistling or hissing: Possibly pressure issues or air in the lines

• Buzzing: Electrical issue with the transformer or relay

Fix it:

• Flush the heat exchanger

• Check water chemistry (especially if you're on well water)

• Call a pro if the sounds don’t stop—don’t wait till it’s too late

Step 9: Check Error Codes (If You’ve Got ‘Em)

Modern boilers have built-in brains. If your Weil-McLain has a display panel, scroll through the fault codes.

• Reference the owner’s manual 

• Look up what each code means—some are simple resets, others need parts replaced

Sometimes, just flipping the power switch off and back on can clear a minor fault.

 

Step 10: Still No Heat? Call for Backup

If you’ve gone through all of the above and still can’t get heat:

• Check if your boiler is under warranty

• Don’t ignore gas smells or carbon monoxide alarms—call the gas company immediately

• Call a licensed HVAC pro if you suspect heat exchanger cracks or control board failure

 

Prevent the Next Cold Snap: Jake’s Heat Survival Tips 🔥

• Do a fall tune-up before the first freeze

• Check water pressure monthly

• Keep spare parts handy (thermostat batteries, flame sensor, pressure gauge)

• Install a freeze alarm or smart boiler monitor if you’re often away

Also, bookmark the Weil-McLain Boiler Collection so you’re not scrambling for replacement options if your system conks out for good.

 

Jake’s Final Word 👋

Listen, stuff breaks. Even solid gear like Weil-McLain boilers. But half the battle is knowing where to look when things go sideways.

With this checklist, you’ve got what you need to keep your system running—or at least get it patched up till a pro can step in. Don’t be afraid to get your hands a little dirty. That’s how you learn—and how you save serious cash. 💪

And hey—if you found this helpful, pass it on to another DIY warrior. Nobody deserves to freeze through February.

Need some maintenance tipsfor your boiler? Visit: Your Seasonal Checklist for a Warmer Home.

Until next time—keep the heat on.
—Jake, your comfort loving tech 🔥🧰