What should an outdoor thermostat do to protect the snow melting system?

To protect the snow melting system, the outdoor thermostat should turn off when the ambient temperature rises above 2°C (35.6°F). This is important because if the temperature is above this threshold, the likelihood of snow accumulation or ice formation is significantly reduced. Keeping the snow melting system running in conditions where it is no longer necessary can waste energy and may lead to unnecessary wear on the system.

By shutting off the system above this temperature, it conserves energy and operational efficiency while still allowing it to function effectively when colder conditions return. The other options, while potentially relevant in different contexts, do not directly pertain to the primary function of preventing unnecessary operation of the snow melting system during milder weather conditions.