Weil-McLain A67 Error — What It Means
The A67 code on a Weil-McLain boiler signals an ignition lockout. The control entered its ignition sequence—sparked or energized the gas valve—but did not detect a stable flame, so it stopped the cycle and locked out to prevent unburned gas from accumulating. In practical terms, something prevented the burner from lighting or the flame sensor from proving that a flame existed.
Because Weil-McLain builds several boiler families (CGa, Ultra, and others) with different controls, the exact fault memory and reset procedure vary by model. Always consult your specific model’s service manual before troubleshooting. The code itself is not a generic failure but a concrete ignition-failure report.
Before You Replace Anything
Homeowners often replace the control board first. Instead, verify gas supply (manual shutoff, inlet pressure, LP tank level) and check the ignitor for cracks or weak spark before swapping electronics.
Common Causes
- Gas supply problem (~35%) Manual shutoff closed, low inlet pressure, empty LP tank, or a service valve stuck shut will prevent any flame.
- Failed or weak ignitor (~25%) A cracked, open, or worn spark electrode will not create a strong enough arc to ignite the gas.
- Dirty or mispositioned flame sensor (~20%) Soot, oxidation, or a bent flame rod prevents the control from proving flame even when the burner lights.
- Gas valve or pilot valve not opening (~10%) The valve may not be receiving the correct signal, or it may be mechanically stuck or failed internally.
- Venting or air-proving interlock open (~7%) A blocked vent, failed air-pressure switch, or open safety limit stops the ignition sequence before gas flows.
- Control board or wiring fault (~3%) Loose connectors, poor ground, or a failed ignition module can interrupt the spark or flame-sense circuit.
Quick Diagnosis
Answer these to narrow it down fast.
Is the manual gas shutoff valve upstream of the boiler fully open?
No: Open the shutoff valve fully, reset the lockout once, and observe whether the boiler lights.
Do you see a strong visible spark at the burner during the trial-for-ignition period?
No: The ignitor is likely failed or not receiving power. Inspect for cracks and measure incoming voltage.
Does the burner briefly light but the boiler locks out anyway?
No: The burner is not lighting at all. Verify gas supply and check whether the gas valve is opening.
Step-by-Step Fix
- Consult your model’s service manual to confirm diagnostic LED patterns and the correct reset procedure for your specific Weil-McLain control.
- Verify gas supply by confirming the manual shutoff is open, the LP tank has fuel (or the natural-gas meter shows flow), and inlet pressure is within spec (consult your model’s table).
- Check venting and safety interlocks by inspecting the exhaust termination for blockage, confirming that all limit switches are closed, and testing the air-proving switch (if equipped) for proper operation.
- Inspect the ignitor for cracks, proper gap to the burner, and incoming voltage during the trial-for-ignition period (many units use 120 volts, but verify your model).
- Clean and inspect the flame sensor by removing the flame rod, polishing it with fine emery cloth or steel wool, and verifying it is straight and properly grounded to the burner.
- Test the gas valve by measuring whether the control sends the correct signal (often 24 V) to the valve coil and listening or feeling for the valve to click open when commanded.
- Clear the lockout by pressing reset once (after the repair) and observe a full ignition cycle under normal call-for-heat to confirm stable operation.
Parts Often Needed
| Part | Notes |
|---|---|
| Ignitor / spark electrode assembly | Amazon | Match the part number in your model’s service manual; igniters vary by boiler family. |
| Flame sensor / flame rod | Amazon | Order the exact replacement rod for your model to make sure correct length and mounting. |
| Gas valve | Amazon | Specify your boiler model and gas type (natural or LP) when ordering. |
When to Call a Pro
Call a licensed HVAC or boiler technician for A67 faults. Gas appliance troubleshooting requires measuring inlet pressure, testing gas-valve operation, and working safely around combustion. A qualified tech will verify venting, air-proving interlocks, and control signals with the proper instruments, then clear the lockout correctly after repair. Attempting DIY gas-system repairs risks explosion, carbon-monoxide hazards, and voiding your warranty.
Rough cost: A pro service call runs about $150–350.