vSMART system reports an 'Outdoor sensor error' or shows no outdoor temperature when one is configured.

Safety warning: Isolate boiler power before working on any wiring. Outdoor sensor circuits are low voltage but may be routed near mains wiring.

Steps to diagnose:

• Check configuration: In the vSMART app or boiler control menu, confirm that an outdoor sensor is actually enabled. If none is installed, disable the option to clear the error.
• Inspect sensor location: Find the Vaillant outdoor sensor on an external wall. Check that the housing is intact and not filled with water or debris.
• Check cable: Follow the sensor cable as far as possible. Look for cuts, crushed sections, or loose junctions. Repair or replace damaged cable.
• Terminal check: With power off, verify the sensor wires are firmly connected to the correct low‑voltage terminals on the boiler or vSMART interface.

If the error remains, the NTC element inside the outdoor sensor is likely faulty. Replace the outdoor sensor with a compatible Vaillant NTC sensor. If unsure, have a Vaillant‑approved technician perform resistance tests and replacement.