If there is no power:
1. Ensure the set temperature is higher than the current water temperature. (see owners manuals for more details)
2. Check breaker or disconnect out by the heat pump to make sure it is in the "ON" position.
3. Check to make sure the breaker in main panel that feeds power to the disconnect or sub panel out by the pool equipment is in the "ON" position.
4. Check that there is water flow to the unit. Most units will have a light indicator with "flow" or "flow error" or the display panel will read "flow".
If the heater reads "flow" check the following:
Unit is running but it is not heating -
How many hours per day is the unit operating? Remember that the heat pump only operates while the pool pump is running. In cooler outdoor temperatures set the time clock to permit 12-24 hour per day operation. After the desired temperature is reached, return the unit to normal operation of 8-10 hours per day.
PLEASE NOTE: Some heat pumps are fitted with a safety time delays and you will have to wait 5 minutes on start up before the heater comes on.
If all of the points above are checked and the Heat Pump is still not working, then