Unplug the unit from its power source.
Determine if the pump is powered. Open the small box located by the outside heat pump to access two circuit breakers protecting the electrical circuits which provide power to the air handler and heat pump condenser. If the unit does not heat, one of these circuits may have tripped. Check both the main electrical panel and any subpanels that supply power to the pump.
Reset the breaker that has tripped if needed, by switching it on to the 'Off' position and then to back on the 'On' position
Remove any debris, leaves or dirt around that unit that may clog its system with a rake or broom.
To clean inside the pump, open the blower access door located on the outside of the unit. Slide the filter from the unit and vacuum inside the compartment with a hand-vacuum hose attachment.
Discard of the older filter and replace it with a new one. Slide it back inside its harness until it stops at the end of the compartment. Change the filter on a monthly basis.
Remove any obstruction like debris from the vents. Shut the access door panel firmly.
Restart the heat pump from a low temperature by turning the system selector knob to emergency heat located in the outside, small box compartment. Wait six hours before returning the unit to its factory setting or normal heat setting.