The Aqua 3000si and 4000si are variant models that come with Full SCALEMASTER Scale Protection. Approximately 60% of the U.K.’s population is supplied with hard water, which can have damaging results on heating elements, and consequently shortens the life of your shower.
Limescale build-up of just 1/8th will reduce heating efficiency by 20%.

Both the SCALEMASTER models come with a 2 YEAR GUARANTEE against effects of limescale build-up

The Aqua 3000si and 4000si have specially coated heating elements that prevent particle adhesion and crystal build-up. An electrolytic inhibitor alters the size and shape of the crystals thus reducing their adhesive properties and allows them to be harmlessly flushed through the system.