Safety first: Turn off power before cleaning coils or opening panels.

Verify setpoint and mode: Confirm the thermostat is set higher than current water temperature and that the heater is in the correct heating mode (not cooling or standby).
Clean evaporator coil: Remove debris from the outdoor coil with a soft brush and low-pressure water. Avoid bending fins.
Check water flow: Ensure valves are fully open and the filter is clean. Adequate flow is essential for heat transfer.
Inspect heat exchanger for scaling: If your pool has hard water and the heater is older, internal scaling may reduce performance. Follow BWT’s descaling procedure or have a technician chemically clean the titanium heat exchanger.
Consider ambient conditions: Heat pumps deliver less heat in cold or very windy conditions. Compare performance to BWT’s capacity charts.

If performance remains poor after cleaning and verifying flow, a refrigeration technician should check refrigerant charge and system pressures.

Pool heater runs but water does not reach set temperature or heats very slowly

Possible Causes