Weil-McLain Boiler A115 Error — What It Means
A115 does not appear in published Weil-McLain fault-code documentation for standard residential or commercial boiler controls. Weil-McLain uses model-specific codes that vary by control family, and the exact meaning must be read from your boiler’s own manual or diagnostics menu. The code may be a misread display, a service-history identifier shown only in the contractor menu, or a code from a different control family. Before troubleshooting, identify your exact boiler model and control type from the rating plate.
If your boiler is locked out or showing a fault, the most common real-world causes across Weil-McLain models are ignition failure, flame-sensor contamination, gas-supply problems, low water pressure, venting or condensate-drainage obstruction, and temperature-sensor faults. Always confirm the exact code in the fault-history menu and verify that the boiler has a valid call for heat before replacing any part.
Before You Replace Anything
Technicians often replace the control board when the real problem is a dirty flame sensor, low gas pressure, or an air-locked heat exchanger. Test ignition components, verify gas supply at 3.5 to 11 inches water column, and purge air from the system before condemning the board.
Common Causes
- Ignition or flame-sensor fault (~30%) A dirty or failed flame sensor, weak ignitor, or intermittent flame signal prevents the burner from lighting or staying lit and triggers a lockout.
- Gas supply problem (~20%) Low gas pressure, a closed manual shutoff, or a failed gas valve stops fuel delivery and the boiler cannot ignite.
- Low water pressure or air in the system (~15%) Insufficient fill pressure or trapped air in the heat exchanger causes false high-limit trips or prevents circulation.
- Venting or condensate obstruction (~15%) Blocked vent pipe, improper vent length, or a clogged condensate trap prevents safe combustion and triggers a safety shutdown.
- Temperature sensor or thermistor failure (~12%) A faulty temperature probe sends incorrect readings to the control, causing short-cycling or lockout on high-limit.
- Control board or wiring issue (~8%) A failed control module, loose connector, or induced voltage from poor grounding produces intermittent faults or false error codes.
Quick Diagnosis
Answer these to narrow it down fast.
Does the display show the exact same code every time, or does it change between resets?
No: An intermittent code suggests a wiring or control-board problem. Check all connectors for corrosion and verify incoming voltage is stable.
Do you hear the ignitor spark or see the burner flame when the boiler tries to start?
No: No ignition means no gas delivery or a failed ignitor. Verify the gas valve is open and gas pressure is between 3.5 and 11 inches water column.
Is the system pressure gauge reading in the normal range (typically 12–15 psi cold)?
No: Low pressure can cause false high-limit trips. Fill the system to the correct pressure and bleed air from the heat exchanger and circulator.
Step-by-Step Fix
- Identify the exact boiler model from the rating plate and locate the matching installation and service manual to decode the fault.
- Enter the diagnostics or fault-history menu on the control (consult your manual for the button sequence) and note the exact code and any sub-codes.
- Verify power and call for heat by confirming incoming voltage at the boiler and checking that the thermostat or zone controller is sending a demand signal.
- Check system pressure on the gauge and fill to the manufacturer-recommended range if low, then bleed air from the heat exchanger and circulator.
- Inspect the ignition system by removing and cleaning the flame sensor with fine sandpaper or a wire brush, and test the ignitor for visible spark or continuity.
- Measure gas supply pressure at the inlet of the gas valve using a manometer to confirm it is between 3.5 and 11 inches water column.
- Examine venting and condensate drainage for blockages, improper slope, or standing water in the trap, and clear any obstructions.
- Test temperature sensors and thermistors with a multimeter for resistance values that match the manual’s table at the current water temperature, and replace any out-of-range probe.
- Replace only the component that fails testing rather than swapping parts at random, and clear the fault history after the repair to confirm the fix.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame sensor (flame rod) | Amazon | Model-specific. Verify the part number from your boiler’s manual or the existing sensor. |
| Ignitor assembly | Amazon | Check whether your boiler uses a spark ignitor or hot-surface ignitor and match the replacement exactly. |
| Gas valve | Amazon | Must match voltage, pressure rating, and connector type. Gas-valve replacement requires a licensed technician. |
| Temperature sensor or thermistor | Amazon | Confirm probe style (immersion well or strap-on) and resistance table from the service manual. |
When to Call a Pro
Call a licensed HVAC or boiler technician immediately if you smell gas, if the boiler vents into living space, or if you are unfamiliar with gas appliances. Gas-valve replacement, control-board diagnostics with advanced metering, and combustion testing require professional tools and certification. A technician can decode model-specific fault codes through the contractor menu, measure combustion efficiency, verify proper venting and condensate drainage, and test electrical components safely. If you have already performed the free checks and the fault persists, professional diagnosis will save time and prevent expensive misdiagnosis.
Rough cost: A pro service call runs about $150–400.