Arrived to call for heat pump not coming on. Upon arrival I had the system call for heat and neither the Y or O terminal at the indoor board or AC were energized. I ensured proper resistance through the O terminal and made sure Y would energize on a call for cooling. The thermostat had failed and was no longer sending communication to the control board during a call for heat pump. I spoke to the customer about this and with his approval replaced the thermostat. I then had the thermostat call for heat, ac, and emg heat with the system performing properly in each. HVAC running upon departure.