Heat Interface Unit Maintenance Checklist

A heat interface unit is the device that connects an individual dwelling or tenancy to a communal or district heating network. It transfers heat from the network to the property's heating and domestic hot water through one or two plate heat exchangers, while keeping the network water hydraulically separate. It typically contains control valves, a differential pressure control, strainers, a heat meter, and the controls that respond to demand.

HIUs matter to network performance out of proportion to their size. A network's efficiency depends heavily on return temperature: the cooler the water returning to the energy centre, the lower the distribution losses and the better the plant performs. An HIU that is fouled, badly controlled, or bypassing raises return temperature, and because the effect is distributed across every unit on the network, a population of underperforming HIUs degrades the whole scheme.

The practical difficulty is access. HIUs are inside occupied dwellings, which makes planned maintenance an appointment and access exercise as much as a technical one, and makes the no-access rate the main limit on how much of the population actually gets maintained.

This checklist is one of 15 in our heating maintenance checklists, covering boilers, calorifiers, heat exchangers, heat pumps and flues — combustion, controls and hot water safety checks.