Mike Here — Let’s Get That Heat Flowing Again 🔧
Alright folks, let’s talk about one of the worst feelings in the dead of winter: your house is freezing, your Weil-McLain boiler is humming… but your radiators? Ice cold.
You spent good money on a name like Weil-McLain because it’s built to last — but even top-tier systems can hit snags. Whether it’s a pilot light gone out, a sensor acting up, or a clogged air vent, I’ve seen just about every reason a boiler stops heating properly. And guess what? Many of them are fixable without a service call if you know what to look for.
Let’s run through the common causes, what you can do on your own, and when it’s time to call in backup.
1. Double Check the Thermostat
It sounds basic, but I’ve been called out dozens of times for a “dead” boiler that turns out to be a confused thermostat.
What to Look For:
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Setpoint too low? Crank it up a few degrees to test response.
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Is the display working? If not, check batteries or wiring.
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Does your thermostat show “HEAT” mode?
If your boiler isn’t getting the signal to fire up, the problem might start here. You can learn more about thermostat issues in this handy Energy Star HVAC guide.
2. Check Boiler Pressure and Water Level
Boilers need water at the right pressure to operate. Weil-McLain recommends around 12–15 psi for most residential systems. If the pressure drops below this, the boiler may not run.
How to Check:
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Look for the pressure gauge on your boiler (often combined with a temperature dial).
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If it’s below 10 psi, you likely need to add water using the fill valve (only if you're comfortable doing so).
If the gauge reads zero, you might have a leak, a broken pressure-reducing valve, or air trapped in the system.
For a deeper dive into how boiler pressure works, check this PlumbNation Troubleshooting Resource, especially if you’re using a low water cut-off control.
3. Is the Pilot Light or Ignition Working?
If your unit is older and uses a pilot light, make sure it hasn’t gone out. Newer Weil-McLain units use electronic ignition — but if that system fails, it can prevent the boiler from firing.
What to Do:
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For standing pilots, try relighting it per the manual’s instructions.
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For spark ignitions, listen for the clicking sound.
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If there’s no ignition, the flame sensor may be dirty or faulty.
Learn how these sensors work from this Flame Sensor Guide from HVAC School.
4. Air Trapped in the Radiators or System
If you’ve recently had your system serviced or refilled, you could have air pockets blocking heat distribution. This is especially common in baseboard and radiator setups.
What to Do:
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“Bleed” the radiators using the bleed valve until water comes out.
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If your system has an automatic air vent, check to make sure it’s working properly.
Don’t forget: if you’re running a multi-zone system, only part of your house may be affected. You can use this Heating System Bleeding Tutorial from Vasco EU as a visual reference.
5. Electrical or Control Board Issues
If nothing else seems wrong and you’re not hearing the unit even try to turn on, the culprit may be electrical:
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A blown fuse or tripped breaker
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A faulty relay
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Issues with the boiler’s control board
Weil-McLain’s newer models like the ECO Tec and Ultra Series have error codes that appear on the LCD display. You can check these codes in your owner’s manual or on Sanford's official troubleshooting guide.
If you see an error like “LOCKOUT 63” or “ERR 29,” it’s usually best to call a professional.
6. Circulator Pump Not Running
The boiler might be heating water just fine — but if it’s not circulating, your radiators stay cold. The circulator pump may be:
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Burned out
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Stuck due to sediment buildup
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Controlled by a faulty thermostat or relay
You might hear it humming but not pushing water. In that case, this isn’t a DIY repair — but it’s good to know what you’re up against when you call the tech.
7. Frozen or Blocked Condensate Line (Condensing Boilers Only)
If you’re running a high-efficiency condensing boiler, it has a plastic condensate drain line. In freezing temps, this line can ice up or clog — which causes a shutdown for safety.
To fix:
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Pour warm (not boiling) water over the outside of the pipe.
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Check for kinks or backflow.
More on this in Automatic Heating’s Tips for Condensate Drains.
Final Thoughts from Mike 🔧
Boilers are like the heart of your home’s heating — and when they stop pumping out heat, everything else grinds to a halt. But the good news is, most of the common problems with Weil-McLain boilers are totally fixable, especially when you know where to look.
Before you start tearing things apart or spending money on a service call, walk through the list above. A little troubleshooting might just save you time, stress, and a whole lot of cold nights.
And if your unit’s old, outdated, or repairs are starting to pile up? You might want to take a look at newer high-efficiency options. You can browse Weil-McLain boilers at The Furnace Outlet — we’ve got models that’ll keep your home cozy and cut down on energy bills.
Need more installation and troubleshooting tips for your boiler? Visit my guide right here!
Stay warm out there. Catch you next time.
- Mike, your cool HVAC neighbor
