An advantage of an electric boiler is that it?

An electric boiler is recognized for its high efficiency of energy transfer from electricity to the boiler water. This is because electric boilers convert electrical energy directly into thermal energy with minimal losses. Unlike fossil fuel boilers, which may waste energy during combustion and heat transfer, electric boilers typically utilize resistance heating, where electricity passes through heating elements to directly heat the water. This direct conversion leads to greater efficiency, resulting in lower energy costs and a more environmentally friendly operation, especially when the electricity is sourced from renewable energy.

The other options, while they may hold certain values in other contexts, do not highlight the primary advantage of electric boilers as effectively. For instance, the notion of being "fail-safe" pertains more to the design and safety measures rather than the inherent efficiency advantage. Similarly, while electric boilers can indeed operate at higher pressures and temperatures or produce superheated steam under specific conditions, these capabilities aren't exclusive advantages that set electric boilers apart from other types of boilers as fundamentally as their high efficiency does.