Reznor 121275 Block or 45-second hot surface ignition

or 45-second hot surface ignition (HSI) control systems

Built with a dry case and a black steel housing

While it is often found in systems with similar nominal voltages

blower wheel

Reznor 121275 Block or 45-second hot surface ignitionThe Reznor 121275 Stack Flue Block is a high limit safety component engineered specifically as an Energy Cutout Device (ECO) for commercial and industrial gas fired heating units. Designed to monitor the integrity of the ventilation system, this blocked vent switch acts as a critical failsafe by measuring exhaust temperatures at the flue. If the sensor detects a restriction, backflow, or overheating condition where temperatures reach the 275F trip