The Harman 3-20-00844 is the correct replacement thermistor probe for Harman pellet stoves manufactured after 2008 that use red lead wires. Ordering by wire color is critical -- two probe versions exist for the Harman lineup and they are not interchangeable. This is the red-wire version (NBK Parts 20087).
The thermistor probe in a Harman pellet stove serves as both a room temperature sensor and an ESP (Exhaust Sensing Probe) monitor, feeding real-time data to the control board. When this sensor degrades or fails, the stove may drop into minimum feed mode, display a fault code, or refuse to maintain a consistent burn -- even though the fire itself is fine.
Replacing the probe with a matched OEM-spec part restores full diagnostic capability and normal automatic operation. This red-wire probe (3-20-00844) is designed as a direct drop-in for any Harman unit produced after 2008 that currently carries red-wired probes.
Red wire version for post-2008 Harman stoves. You must match your existing probe wire color -- red for red, do not substitute the black-wire version.
Rated to 527 deg F, providing reliable sensing across the full operating temperature range of Harman pellet stoves.
Works with the stove's built-in automatic diagnostic circuit that continuously monitors the ESP and room sensor for faults during operation.
If a sensor fault is detected, the control board alerts the user and shifts the stove to minimum feed and minimal burn to protect the unit.
Harman produces two thermistor probe variants for their post-2008 pellet stove lineup. The only external difference is the color of the lead wires. The internal sensor characteristics, however, differ between versions -- installing the wrong probe color will result in incorrect temperature readings, fault codes, or improper stove behavior.
This probe is compatible with a wide range of Harman brand pellet stoves manufactured after 2008. Harman models known to use thermistor probes in this generation include:
The thermistor probe communicates continuously with the Harman control board, reporting both room ambient temperature and exhaust-side heat levels. The control board uses this data to modulate the feed rate, combustion blower speed, and distribution blower output. A faulty or degraded probe is one of the most common causes of unexplained fault codes, inconsistent heat output, and "minimum burn" lockouts in Harman pellet stoves.