NasGas Geyser Semi 404Plus Solar Friendly SeriesDiscription. Semi Instant Heating: This unit operates by keeping a small amount of water pre heated in its tank, which can deliver hot water faster than a traditional storage geyser, while still being more efficient than a purely instant model. Solar Friendly Design: The primary benefit of this series is its compatibility with solar water heaters. It accepts pre heated water from a solar system, requiring the electric element to do less work to reach