What should be checked first if a heat pump is not heating properly?

When diagnosing a heat pump that is not heating properly, the thermostat settings should be checked first because they control the operation of the system. If the thermostat is set incorrectly—such as being in a cooling mode instead of heating, being set to a lower temperature than the current room temperature, or not functioning at all—the heat pump will not activate or provide the required heating. Ensuring the thermostat is properly set and functioning can quickly resolve many heating issues.

While insulation levels, the age of the unit, and duct sizes are important factors that can impact the overall efficiency and performance of the heating system, these should be assessed only after confirming that the thermostat is correctly set. If the thermostat is malfunctioning or set incorrectly, the system won't operate as intended, regardless of the condition of the insulation or ductwork. This makes checking the thermostat the immediate priority in troubleshooting heating issues with a heat pump.