Why do HVAC techs hate Nest thermostats?

HVAC technicians often express frustration with Nest thermostats primarily because of the absence of a dedicated C-wire (common wire) in many retrofitted installations, which forces the thermostat to draw power by "power-stealing" small voltage pulses through the heating and cooling equipment relays. This improper power-stealing frequently causes HVAC system relays to chatter, compressors to short-cycle, and furnace control boards to burn out prematurely. Additionally, techs encounter frequent service calls where incorrect self-learning schedules or misconfigured wire mapping lock up heat pumps. Verification: Inspect your thermostat subbase wiring terminal block to confirm that a dedicated blue C-wire is securely connected to the 'C' terminal on both the thermostat and the HVAC control board.