If you live in a modern apartment complex or a development with a communal heating system, you likely have a Caleffi Heat Interface Unit (HIU). Usually tucked away in a utility cupboard, this white or grey box is the "engine room" of your home's heating and hot water.

While Caleffi units are known for being reliable, they can occasionally run into hiccups. If your morning shower is more "lukewarm" than "steaming," here is a quick guide to understanding what’s going on and how to fix it.

Choosing the right Heat Interface Unit (HIU) engineer can save you time, money, and stress. HIUs are complex systems that require specialist knowledge — not just general plumbing skills. In this guide, we explain how to select the best HIU engineer in London, what qualifications to look for, and why reputation, experience, and transparent pricing matter.