Weil-McLain A160 Error Code — What It Means
A160 (also displayed as A-16 or A16) on a Weil-McLain AquaBalance boiler is not a fault code for a broken part. It appears at power-up when the control expects an outdoor temperature sensor but none is installed. This code is specific to central-heating-only boiler configurations that require the outdoor sensor for proper modulation and setup. The boiler will not run until the sensor is installed and the control is reset.
This is different from a failed sensor. If the outdoor sensor is installed but faulty or disconnected, the AquaBalance control will display F-39 instead. A160 strictly means the sensor is absent during initial commissioning or after a control replacement where the sensor was not connected.
Before You Replace Anything
Some technicians assume A160 means a bad sensor and replace it, but the code actually means the sensor is missing entirely. Check the sensor terminals at the control harness before ordering any parts.
Common Causes
- Outdoor sensor not installed (~70%) The AquaBalance control on a central-heating-only boiler requires an outdoor sensor, but it was never wired during commissioning or after a control replacement.
- Wrong boiler setup or commissioning error (~20%) The control was configured for a mode that expects the outdoor sensor, but the installer omitted it or selected the wrong dip-switch settings.
- Sensor wiring disconnected at terminals (~8%) The outdoor sensor was installed originally but the two-wire connection came loose or was removed during service work.
- Control module replaced without sensor reinstall (~2%) A technician swapped the AquaBalance control board and forgot to reconnect the outdoor sensor leads.
Quick Diagnosis
Answer these to narrow it down fast.
Is an outdoor sensor physically wired to the boiler control terminals?
No: The sensor is missing. Install the correct Weil-McLain outdoor sensor for the AquaBalance system and reset the control.
Does the control display clear after you press the reset button for 1.5 seconds?
No: The sensor is still not detected or the wiring is incorrect. Verify the sensor model and terminal connections, then call a technician.
Is this a new installation or a recent control board replacement?
No: The sensor may have been disconnected during service work. Inspect the wiring harness for loose or missing connections.
Step-by-Step Fix
- Confirm the exact error code displayed on the AquaBalance control to verify it reads A-16, A16, or A160, not a different alarm like F-39.
- Inspect the control module and boiler terminals to check whether an outdoor sensor is physically installed and connected to the sensor input on the control harness.
- If no sensor is installed, obtain and install the correct Weil-McLain outdoor sensor for the AquaBalance system, following the wiring diagram in the installation manual for sensor terminal polarity and location.
- Reset the control by pressing and holding the reset button on the AquaBalance module for approximately 1.5 seconds to clear the A16 code.
- Initiate a call for heat by raising the thermostat setpoint and verify the boiler enters normal run mode without the code reappearing.
- If the sensor is already installed but the code persists, check the sensor wiring for continuity, verify the sensor type matches the control’s requirements, and measure the sensor resistance to rule out a true fault (which would produce F-39).
- Consult the boiler’s setup configuration or dip-switch settings if the code returns, as the control may be set for a mode that does not require the outdoor sensor, or the wrong sensor type was installed.
Parts Often Needed
| Part | Notes |
|---|---|
| Weil-McLain outdoor temperature sensor (AquaBalance) | Amazon | Two-wire sensor for AquaBalance controls on central-heating-only boilers. Verify compatibility with your exact boiler model before ordering. |
| Outdoor sensor wiring harness | Amazon | If the original sensor leads are cut or damaged, a replacement harness may be needed to connect the sensor to the control terminals. |
When to Call a Pro
Call a licensed heating technician if you are not comfortable working with boiler control wiring or if the sensor is already installed and the code will not clear after reset. Installing the outdoor sensor requires identifying the correct control terminals, running low-voltage wiring to an exterior wall location, and configuring the AquaBalance control for proper outdoor reset modulation. If the code persists after sensor installation, the technician will need to verify sensor resistance, check for short circuits in the wiring, and rule out a control board fault. Gas-fired boiler work also requires proper venting, combustion analysis, and knowledge of local codes, so professional installation and commissioning are recommended for any new sensor or control replacement.
Rough cost: A pro service call runs about $150-$300.