GOOGLE NEST NEST THERMOSTAT (2020/4TH GEN) Error E298 No Power

3-Amp / 5-Amp Automotive Blade Fuse

The HVAC control board utilizes a low-voltage fuse to protect the 24V transformer from shorts. If this fuse blows due to a transient surge or a short in the thermostat wiring, the Nest will lose all power and trigger the E298 code immediately as the R-wire becomes de-energized.

HVAC Condensate Float Switch

This safety device is wired in series with the thermostat's power wire. When a condensate drain line clogs, the rising water level mechanically lifts a float, opening the electrical contacts and breaking the 24V circuit to the thermostat to prevent HVAC operation and subsequent flooding.

Furnace Door Interlock Switch

Modern furnace cabinets feature a spring-loaded momentary switch that must be physically depressed by the blower compartment panel. If the panel is loose or the switch's internal spring mechanism fails, the high-voltage supply to the transformer is cut, effectively killing power to the Nest.