How we diagnose an HIU fault
We start at the primary side. If the flow temperature arriving at the unit is below design, nothing inside the HIU can fix that and the fault belongs to the network, not the flat. If the primary is correct but the secondary is cool, the heat exchanger or the control valve is at fault. If both sides look right but the resident still has no hot water, we look at the flow switch, the sensor and the controller. Working in that order avoids replacing sound components.
- Primary flow and return temperature at the unit
- Secondary DHW and heating temperatures under draw-off
- Differential pressure across the primary connections
- Strainer condition on both sides
- Actuator response to a demand signal
- Sensor, flow switch and PCB checks
