Weil-McLain A110 Error — What It Means
A110 does not appear in published Weil-McLain boiler control documentation. The closest manufacturer-documented fault is A01, which means no burner ignition on Aqua Balance controls. If your display shows A110, it may be a misread screen, a model-specific service value, or a different control platform altogether. The safe approach is to identify your exact boiler model and control type before treating A110 as a fault code.
If the code is actually A01, Weil-McLain defines it as a condition where the boiler fails to establish flame after a heat call. After repeated ignition attempts, the control enters lockout and displays A01. Common causes include no gas supply (especially on new installs or after purging), faulty ignition or flame-detection electrode, failed gas valve, insufficient gas pressure (specified as 3.5 to 11 inches water column for Aqua Balance systems), dirty heat exchanger from overdue maintenance, or a blocked condensate trap.
Before You Replace Anything
Many technicians replace the gas valve first when A01 appears, but the electrode assembly (ignition and detection) fails more often and costs much less. Observe whether a spark occurs during a heat call before ordering a valve.
Common Causes
- Ignition or detection electrode fouled or failed (~40%) Carbon buildup, corrosion, or a cracked ceramic insulator prevents spark or blocks the flame signal, triggering lockout after three attempts.
- No gas or insufficient gas pressure (~25%) On new installations or after line work, air in the gas piping or supply pressure below 3.5 inches water column stops ignition completely.
- Failed gas valve (~15%) An internal coil failure or stuck diaphragm prevents gas flow even when the control sends voltage to the valve.
- Blocked or improperly installed condensate trap (~10%) A dry, reversed, or clogged trap disrupts combustion airflow and causes flame instability or rollout, leading to lockout.
- Dirty heat exchanger or venting issue (~10%) Soot or scale accumulation restricts combustion and prevents reliable flame sensing, especially when combined with insufficient makeup air.
Quick Diagnosis
Answer these to narrow it down fast.
Do you see or hear a spark when the boiler calls for heat?
No: The ignition electrode or its wiring is likely bad. Inspect the electrode for cracks or carbon buildup, check the wire connection at the control board, and test the ignition transformer if accessible.
Is the gas supply valve fully open and has the line been purged recently?
No: Open the manual shutoff fully. On new installs or after gas work, purge air from the line at the union upstream of the boiler until you smell gas, then reconnect and reset.
Does the boiler light briefly then go into lockout?
No: The boiler never ignites. Focus on gas supply, gas valve, and ignition spark first before inspecting the sensor circuit.
Step-by-Step Fix
- Confirm the exact code. Take a clear photo of the display or write down the model number and control type (Aqua Balance, Evergreen, Ultra, etc.) from the boiler nameplate and the control label.
- Reset the boiler. Press and hold the reset button on the control for 1.5 seconds, then wait for a heat call to begin. Listen and watch for a spark clicking sound and observe whether flame appears.
- Check gas supply. Verify the manual gas shutoff valve upstream of the boiler is fully open. On a new installation or after recent gas work, crack the union upstream of the boiler gas valve to purge air until you smell gas, then retighten and reset.
- Inspect the ignition and flame-detection electrode. Remove the electrode assembly from the burner chamber. Look for cracks in the ceramic insulator, carbon or soot on the probe tip, and corrosion on the wire connection. Clean the tip with fine-grit sandpaper or replace the assembly if damaged.
- Measure gas supply pressure. If you have a manometer, connect it to the test port on the gas valve inlet and confirm supply pressure is between 3.5 and 11 inches water column during a call for heat. Low pressure indicates a regulator or utility supply problem.
- Test the gas valve. With the boiler calling for heat, use a multimeter to verify the control is sending voltage to the valve coil (typically 24 VAC). If voltage is present but no gas flows, replace the gas valve.
- Check the condensate trap and venting. Pull the trap and verify it has water in the bend, is installed in the correct orientation per the manual, and is not clogged. Inspect the intake and exhaust vent terminations outdoors for blockage, ice, or reversed piping.
Parts Often Needed
| Part | Notes |
|---|---|
| Ignition and flame-detection electrode assembly | Amazon | Match the part number on your boiler’s service label or manual; rod length and thread pitch vary by burner model. |
| Gas valve | Amazon | Order by boiler model and fuel type (natural gas or propane); valve voltage and pressure regulator settings are model-specific. |
| Condensate trap kit | Amazon | Replace if cracked or if the original was installed backward; some Weil-McLain models use a trap integral to the collector box. |
When to Call a Pro
Call a licensed technician if you are unfamiliar with gas appliances, do not own a manometer to measure gas pressure, or cannot safely access the electrode and burner chamber. Any work on gas piping, gas valves, or combustion components carries risk of gas leak, carbon monoxide exposure, or fire. A technician will also verify proper venting, condensate drainage, and control settings that are not adjustable by the homeowner. If the boiler repeatedly locks out after your reset attempts or you smell gas at any point, shut off the manual gas valve and call for service immediately.
Rough cost: A pro service call runs about $150-350.