A direct OEM-style replacement vacuum switch engineered for compatible Harman pellet stoves. This pressure-sensing switch monitors combustion airflow and closes the ignition and feed circuit at a calibrated .10 inches water column (WC), helping your stove run safely and efficiently. If your pellet stove is failing to ignite, shutting down unexpectedly, or not feeding pellets correctly, a faulty vacuum switch is a common cause -- and this is the factory-spec replacement.
The Harman 3-20-6866 is a differential pressure sensor vacuum switch designed to verify that adequate combustion airflow is present before allowing the ignition circuit and auger feed circuit to operate. This is a critical safety and performance component: if the exhaust blower is not producing sufficient draft, the switch remains open and prevents the stove from firing or feeding pellets -- protecting against incomplete combustion and smoke rollout.
Calibrated to close at .10 WC, this switch matches the factory specification for the Harman models it serves. It is also cross-listed as NBK Parts number 20168, making it straightforward to verify you have the correct part when sourcing through multiple suppliers.
Closes the ignition and pellet feed circuit at precisely .10 inches water column (WC) -- matching Harman OEM specifications.
Default position is open (NO). The switch closes only when sufficient negative pressure is confirmed from the combustion blower.
Controls both the ignition circuit and the auger feed circuit, preventing pellet delivery and ignition attempts without confirmed airflow.
Also listed as NBK Parts 20168, simplifying identification and verification across parts suppliers and service databases.
Pellet stoves rely on a combustion blower to draw air through the burn pot and exhaust gases out through the flue. The vacuum switch is plumbed into this airflow path via a small silicone or rubber hose. When the blower spins up and creates negative pressure (vacuum) above the .10 WC threshold, the switch closes -- signaling the control board that it is safe to energize the igniter and the auger motor. If the switch never closes (due to a blocked flue, failed blower, clogged hose, or a failed switch itself), the stove will not light and will not feed pellets.
Replacement is typically straightforward for a homeowner comfortable with basic appliance service. The switch is accessible from the control compartment on most compatible Harman models. Disconnect the vacuum hose and the two electrical leads, then remove the mounting fasteners. Install the new switch in reverse order. No calibration is required -- the switch is factory-set. Always allow the stove to cool completely before servicing.