Weil-McLain A118 Error Code — What It Means
A118 is not a verified standard fault code in Weil-McLain manufacturer documentation. Weil-McLain boilers use model-specific and control-specific fault codes, so the exact meaning depends on your boiler model and the control platform installed. The code may appear in the fault-history menu on newer units, but without the service manual for your exact model you cannot safely interpret it.
To find the correct meaning, locate your boiler’s model number and control type, then pull the installation and service manual (often available on the Weil-McLain website or from your installer). The manual will have a fault-code table that defines A118 for your control. Do not attempt repairs based on generic code lists from other models, because the same alphanumeric code can mean entirely different things across different Weil-McLain product lines.
Before You Replace Anything
Without the correct manual, technicians sometimes replace control boards when the real fault is a loose connector or failed temperature sensor. Always pull the fault history from the boiler’s diagnostic menu and test sensors with a meter against the manufacturer’s resistance table before ordering a board.
Common Causes
- Model-specific fault code (~100%) A118 is not confirmed in manufacturer sources and may be unique to your control platform or may not exist at all, so the true cause cannot be determined without the correct service manual.
- Temperature sensor failure On many Weil-McLain controls, faults related to supply or return water temperature (such as E18 for over-temperature) are caused by a failed thermistor or damaged sensor wiring.
- Loose or corroded sensor connector Wiring faults at the sensor plug or at the control board can mimic a sensor failure and generate fault codes on modern Weil-McLain controls.
- Flame-sensing or ignition component fault Some Weil-McLain codes (such as E03) point to dirty or failed flame rods, ignition electrodes, or gas-valve issues, though A118 is not verified to fall in this category.
Quick Diagnosis
Answer these to narrow it down fast.
Does your boiler's service manual or wiring diagram list code A118?
No: The code may be a firmware-specific or non-standard entry. Contact Weil-McLain technical support or a licensed technician with your model and serial number to confirm the fault definition.
Is the fault shown as 'current' or 'active' in the boiler's fault-history menu?
No: The fault was historical and may have cleared. Monitor the boiler for recurrence and note the operating conditions when it logged.
Have you already reset the fault more than twice and it returned each time?
No: Perform one careful reset after confirming safe operating conditions (gas on, power on, system pressure normal), then watch for recurrence.
Step-by-Step Fix
- Shut off power at the service switch or breaker and confirm the boiler is off. If you smell gas or see unsafe conditions, leave the area and call a professional immediately.
- Locate your boiler’s model and serial number (usually on a label inside the jacket or on the control panel) and download the installation and service manual from the Weil-McLain website or request it from your installer.
- Enter the diagnostic or fault-history menu on your boiler’s control (the manual will show the button sequence) and note whether A118 is listed as a current fault or a historical fault, and whether it requires manual reset or auto-reset.
- Consult the fault-code table in your service manual to find the exact definition of A118 for your model and control, along with the manufacturer’s recommended diagnostic steps and the component or sensor to inspect.
- Inspect wiring and connectors at the suspect sensor and at the control board for loose pins, corrosion, or damage. Reseat all connectors firmly and look for burnt or chafed wires.
- Test the suspect sensor (if the manual identifies one) with a multimeter set to resistance, and compare the reading to the manufacturer’s resistance-versus-temperature table in the service manual. Replace the sensor if it reads open, shorted, or out of spec.
- Restore power, refill and purge air if you opened any part of the system, then run the boiler and confirm the fault does not return. If the code reappears or if you cannot locate the manual definition, call a licensed boiler technician for model-specific diagnosis.
Parts Often Needed
| Part | Notes |
|---|---|
| Temperature sensor / thermistor | Amazon | Only if your manual identifies A118 as a sensor fault and testing confirms the sensor is out of spec. Match the exact part number for your control. |
| Wiring harness or connector | Amazon | If inspection reveals melted, corroded, or damaged wiring at the sensor or control board. Order the OEM harness for your boiler model. |
When to Call a Pro
Call a licensed boiler technician immediately if you cannot locate the service manual for your exact model, if the fault-history menu does not list A118, or if you are unsure which control platform is installed. Also call a pro if you have inspected wiring and sensors but the fault returns after reset, if you lack a multimeter and the skill to test sensor resistance safely, or if the boiler shows any other symptom such as lockout, flame failure, or unusual noises. Gas-fired boiler work requires proper combustion analysis and safety checks that are beyond DIY scope. Never repeatedly reset a recurring fault without diagnosing the root cause, because some faults protect against dangerous conditions like overheating or gas-valve failure.
Rough cost: A pro service call runs about $150-400.