Low-temperature checklist: what to check when the heat pump is underperforming

When efficiency drops in cold weather, an organized inspection is required before making changes to setpoints or parameters.

1. External exchanger

Check for ice, debris, and free airflow.

2. Defrost

Record if it starts, how long it lasts, and if it clears the ice completely.

3. Water temperatures

Check supply, return, and ΔT.

4. Water flow

Check the circulator, filters, valves, and minimum required flow.

5. Sensors

Compare outdoor air, coil, and water readings with independent measurements where possible.

6. Auxiliary heating

Confirm if it activates correctly when actual conditions require it.