The heat pump is running but providing low heat: a complete checklist

When the unit is operating without an obvious alarm but thermal output is low, a combined diagnosis is needed.

1. Water temperatures

Check supply, return, and actual ΔT.

2. Water flow

Very low or excessively high flow can distort performance.

3. External conditions

Available power must be compared against performance tables at the specific temperature.

4. Refrigerant circuit

Check pressures, superheat, EEV, and compressor operation.

5. Consumption

Electric power in relation to thermal output helps to determine if the problem is truly in the heat pump or in the distribution system.