If your St. Croix pellet stove is shutting down prematurely, failing to ignite, or throwing a fault code related to flame detection, the proof of fire switch is a common culprit. The 80P20038-R is the correct OEM-spec replacement switch for a wide range of St. Croix pellet stove models, sold under NBK Parts number 20159. At just 0.1 lb., it is a lightweight but critical component that tells the stove's control board that combustion has been successfully established.
The proof of fire switch -- sometimes called a flame sensor switch or fire detection switch -- is a safety and control component that monitors whether your pellet stove has successfully achieved ignition. Once the stove lights, this switch signals the control board to transition from ignition mode to run mode. If the switch fails or loses calibration, the stove may shut down during startup even when fire is present, or in rarer cases, may fail to detect a lost flame during operation.
Replacing a faulty proof of fire switch is a straightforward repair that restores normal ignition sequencing and prevents nuisance shutdowns. The St. Croix 80P20038-R is the correct part for the models listed below and is also cataloged as NBK Parts 20159 for cross-reference purposes.
Fits 16 St. Croix pellet stove models spanning multiple product generations, including inserts and freestanding units.
Designed to meet the original equipment specification for the 80P20038-R switch position on St. Croix stove control systems.
Weighs only 0.1 lb. -- a small part that plays a big role in startup sequencing and safe stove operation.
Also cataloged as NBK Parts 20159, making it easy to verify compatibility when sourcing through multiple suppliers.
During startup, your St. Croix pellet stove runs its igniter and auger through a timed ignition sequence. The proof of fire switch detects that combustion has actually occurred -- not just that the igniter is hot. Once it confirms fire, the control board advances to normal run mode, increasing auger feed and combustion air to the operating set point.
If the switch is faulty, the board never receives the confirmation signal. The stove will run through its ignition cycle and then shut down and display an ignition failure or proof of fire fault. Replacing the switch with a fresh 80P20038-R restores that signal path.
The proof of fire switch is typically located in or near the combustion area of the stove. Before replacing it, power down the stove completely and allow it to cool. Disconnect the electrical connector from the old switch, remove the mounting hardware, install the new switch in the same orientation, reconnect the wiring, and run a test ignition cycle to confirm proper operation. Refer to your stove's wiring diagram to confirm the correct connector orientation for your specific model.
The 80P20038-R proof of fire switch is confirmed to fit the following St. Croix pellet stove models: