Weil-McLain A134 Error Code — What It Means
A134 is typically an ignition failure or flame-not-proven fault. The boiler control started the burner sequence but did not detect a valid flame signal, so it stopped the heat call and locked out or entered retry mode. The exact on-screen text and code mapping can vary by Weil-McLain model and control family, so always confirm the code in your unit’s service manual before replacing parts.
In practical terms, the control is not satisfied that flame is present after the ignition attempt. This can happen because gas never reached the burner, the ignitor did not light the gas, or the flame sensor did not detect the flame even though combustion occurred.
Before You Replace Anything
Homeowners often replace the gas valve or control board first. Clean and test the flame sensor and verify the ignitor is glowing or sparking before buying expensive parts.
Common Causes
- Dirty or failed flame sensor (~35%) Carbon deposits or corrosion on the flame-sensing probe prevent the control from verifying flame presence even when the burner lights.
- Failed hot-surface ignitor or spark ignitor (~30%) The ignitor does not glow hot enough or produce a spark, so the gas never ignites during the startup sequence.
- No gas flow to the appliance (~15%) The gas shutoff is closed, the supply line is shut off upstream, or the meter valve is off.
- Gas valve not opening (~10%) The gas valve does not receive power from the control, has a failed coil, or is mechanically stuck closed.
- Wiring or connector problem (~7%) Loose, corroded, or damaged connections in the ignition or flame-proving circuit interrupt the signal or power.
- Control board issue (~3%) The ignition control or boiler control board has a failed relay or flame-detection circuit that prevents proper startup sequencing.
Quick Diagnosis
Answer these to narrow it down fast.
Does the ignitor glow bright orange (hot-surface) or produce a visible spark during the startup attempt?
No: The ignitor has failed or is not receiving power. Check wiring and replace the ignitor.
Can you hear or smell gas at the burner when the valve should be open?
No: No gas is flowing. Verify the gas shutoff is open and check the gas valve.
Does the fault repeat immediately after a single reset?
No: A one-time fault may have been a transient issue, but monitor closely for recurrence.
Step-by-Step Fix
- Verify the exact model and control family by reading the serial plate and checking the service manual to confirm A134 is an ignition fault on your unit.
- Check the gas supply by confirming the shutoff valve at the boiler and upstream at the meter are fully open and that other gas appliances in the building are operating.
- Inspect the ignitor by observing a startup cycle and verifying the hot-surface ignitor glows bright orange or the spark ignitor produces a strong spark.
- Clean the flame sensor by removing the sensing probe, wiping it gently with fine steel wool or emery cloth to remove carbon deposits, and reinstalling it with a clean, tight connection.
- Check wiring and connectors at the ignitor, flame sensor, gas valve, and control board for looseness, corrosion, or damage, and reseat all plugs firmly.
- Access the fault history on the control (if available) to confirm the lockout is ignition-related and to see if there are other stored codes.
- Reset once after correcting the cause and observe a full startup cycle to verify ignition and flame proving, but do not repeatedly reset without finding and fixing the fault.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor (flame-sensing electrode) | Amazon | Match the part number to your Weil-McLain model and control family. |
| Hot-surface ignitor | Amazon | Confirm the ignitor type (silicon-nitride or silicon-carbide) and voltage from the boiler’s parts list. |
| Gas valve | Amazon | Order by model and serial number if the valve does not open or has no voltage at the coil. |
| Ignition control board | Amazon | Replace only after testing all other ignition and flame-proving components. |
When to Call a Pro
Call a professional immediately. A134 involves the gas ignition and flame-proving system, which requires a trained technician to safely diagnose and repair. Repeated lockouts without finding the root cause can damage the control or create unsafe conditions. The technician will use combustion-analysis tools, a multimeter, and the model-specific service manual to test ignitor current draw, flame-sensor microamperage, gas valve operation, and control-board outputs. Work on gas-fired equipment must comply with local codes and should be performed by a licensed technician.
Rough cost: A pro service call runs about $150-350.