Viessmann 7828749 Flow Sensor 321894 708 Stick with genuine OEM HVAC Stick with genuine OEM HVAC parts to ensure full communication with the central control board and avoid the surging issues common with sub par aftermarket alternatives this SWT1276 thermal switch offers the repeatability required to restore safe furnace operation without the nuisance tripping seen in lower quality aftermarket alternatives OEM Compatibility: Guaranteed fit for Viessmann B1KA combi boilers and CPK series models without field modifications This sensor is specifically designed for integration into Viessmann B1KA and Viessmann CPK systems