OEM Lennox Relay — 10P21

The genuine OEM Lennox 10P21 relay is an electrically operated switch that controls power to key components in your Lennox furnace or air handler — such as the blower motor, fan, or auxiliary heat. When the low-voltage control circuit energizes the relay coil, its contacts close to route line-voltage power to the connected load, allowing your thermostat to safely command high-current devices. This relay is engineered to the exact specifications required for reliable operation in Lennox equipment.

Common failure symptoms include a blower or fan that will not start, intermittent operation, an audible buzzing or chattering from the control box, pitted or welded contacts, or a burnt-electrical smell near the relay. A failed 10P21 often leaves the system with control power but no output to the driven component.

Why OEM matters: Lennox systems are designed around precise coil voltages and contact ratings. An OEM 10P21 relay guarantees the correct pull-in voltage, contact amperage, and physical fit — protecting downstream motors and boards from the arcing and voltage irregularities that off-spec substitutes can cause. Choosing the factory-authorized part means a direct, trouble-free replacement and rated performance for the life of your Lennox equipment.