Can I replace this without draining the system

it is compatible with the Watts Series 1000 float valves

High-Temperature Durability: Engineered with materials capable of withstanding the thermal stresses common in furnace and water heater combustion chambers

It is compatible with a wide range of models under the Tempstar

What causes this switch to trip

Field Controls 46282800 Relay Can I replace this withoutThe Field Controls 46282800 is a dedicated fixed post purge timer relay designed for precise flue gas evacuation in power venting systems. This critical component ensures that the power venter motor continues to operate for a set duration after the burner cycle completes, effectively clearing residual combustion products and preventing heat soak in the heat exchanger. Engineered for compatibility with Field Controls PVG series power venters and CK 43F