Heat Interface Unit (HIU)

This is the other piece of equipment that requires an external party to service it.  The good news is that it costs you nothing to do this.  This is because this unit belongs to E-On who have the contract to supply hot water to the building.  E-On therefore maintain the unit, and carry out an annual servicing for free.   They usually contact you as it nears the anniversary of the last service but you can also contact them on 0345 302 4312.