No heat on a heat pump. Reversing valve not being energized when thermostat is calling for heat. System was running in cooling mode. Bypassed thermostat, and heat worked. Got power to the reversing valve. I reset the thermostat , to factory standard , and heat works. Tested system in heating and cooling multiple times, with no issue at this time. It’s possible the thermostat is going bad. Told customer to monitor, and if it happens again, ecobee thermostat will need to be replaced. No diagnostic fee. We were at the house for home care in September.