Weil-McLain A112 Error — What It Means
There is no official Weil-McLain error code listed as A112 in manufacturer documentation. This appears to be a misinterpretation of a model number (such as CGa-112 or Ultra-112) mixed with a diagnostic code, or confusion with the E01/E02 ignition fault series. The symptoms described in user forums for “A112” (boiler shuts down after lighting) align with standard E01 (Ignition Failure/Lockout) or E02 (Flame Loss) fault codes.
These faults mean the burner lit successfully but could not maintain a stable flame for the required duration (typically 3 to 5 seconds). The control system detected no flame signal from the flame sensor, shut off the gas valve, and entered lockout mode to prevent unsafe operation.
Before You Replace Anything
Many homeowners replace the gas valve or ignitor when the actual problem is a dirty flame sensor that costs under $5 to clean with steel wool.
Common Causes
- Dirty or corroded flame sensor (~45%) The sensor tip is coated with carbon, oxidation, or debris and cannot detect the flame current, causing the control to shut down.
- Weak or interrupted gas flow (~20%) Low gas pressure from the utility or regulator, a partially closed supply valve, or a clogged gas filter prevents stable combustion.
- Obstructed intake or exhaust vents (~15%) Bird nests, ice, or condensation buildup block the vents and cause the flame to sputter or be forced out.
- Flame sensor wiring or grounding issues (~10%) Loose wiring connections, poor boiler grounding, or a failed sensor prevent flame detection even when the flame is present.
- Blocked condensate trap (~10%) In condensing models like the Ultra series, a clogged trap causes pressure imbalance that forces the flame out or makes the sensor fail.
Quick Diagnosis
Answer these to narrow it down fast.
Does the boiler light and then shut down within a few seconds?
No: The burner may not be lighting at all. Check gas supply, ignitor, and control board.
After cleaning the flame sensor, does the boiler run normally for a full heating cycle?
No: Check gas pressure with a manometer or inspect venting for blockages. Call a technician if you lack tools.
Is there visible soot, rust, or white residue on the burner or heat exchanger?
No: Focus on electrical components and gas supply. Test flame sensor wiring and verify proper grounding.
Step-by-Step Fix
- Turn off power at the boiler switch, wait 30 seconds, and turn it back on to attempt a reset and observe if the fault repeats.
- Remove the flame sensor (or flame rod) assembly from the burner area following the boiler’s service manual.
- Clean the sensor tip gently with fine steel wool or abrasive paper to remove all carbon, oxidation, and debris, then reinstall it aligned with the burner flame path.
- Verify gas supply by confirming the shut-off valve is fully open, propane tanks are not empty, and using a manometer to measure inlet and manifold gas pressure against the boiler’s specification.
- Inspect intake and exhaust vents for birds, ice, condensation, or debris and clear any blockages.
- Check condensate trap (on Ultra or other condensing models) by removing it, cleaning out debris, and flushing with vinegar if gunk is present.
- Test electrical connections by verifying flame sensor wiring is secure, the boiler is properly grounded, and replacing the sensor if resistance or continuity tests fail.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor (flame rod) | Amazon | Match the exact model number of your Weil-McLain boiler for correct fit. |
| Gas valve | Amazon | Only needed if pressure tests and sensor cleaning do not resolve the fault. |
When to Call a Pro
Call a licensed technician if you are uncomfortable working with gas appliances, if the flame sensor cleaning and vent inspection do not resolve the lockout, or if you lack a manometer to measure gas pressure. A professional should handle any gas valve replacement, control board diagnostics, or combustion analysis. Intermittent flame loss can also indicate heat exchanger cracks or blocked flue passages that require a thorough inspection and combustion testing to diagnose safely.
Rough cost: A pro service call runs about $150-300.