{"product_id":"viessmann-7861491","title":"Viessmann 7861491 Flame Sensor","description":"\u003cp\u003eWhen you're troubleshooting a \u003cstrong\u003eViessmann Vitodens\u003c\/strong\u003e unit that keeps hitting an \u003cstrong\u003eF2 flame loss\u003c\/strong\u003e or \u003cstrong\u003eL2 ignition lockout\u003c\/strong\u003e, your first check should be the \u003cstrong\u003eViessmann 7861491 Flame Sensor\u003c\/strong\u003e. Also known as an \u003cstrong\u003eionization electrode\u003c\/strong\u003e, this \u003cstrong\u003enickel-iron (NiFe)\u003c\/strong\u003e component is the backbone of the \u003cstrong\u003eflame rectification\u003c\/strong\u003e circuit. It’s engineered specifically for \u003cstrong\u003eCM2 series boilers\u003c\/strong\u003e, including models like the \u003cstrong\u003eCM20490\u003c\/strong\u003e, \u003cstrong\u003eCM20491\u003c\/strong\u003e, and \u003cstrong\u003eCM20493\u003c\/strong\u003e. This isn't just a dummy rod; it’s a precision \u003cstrong\u003eHVAC safety device\u003c\/strong\u003e that must prove a stable \u003cstrong\u003emicro-amp signal\u003c\/strong\u003e—typically between 2 and 6 μA—back to the \u003cstrong\u003econtrol board\u003c\/strong\u003e within seconds of the gas valve opening. \n\nIf this sensor is fouled by carbon buildup or has a cracked \u003cstrong\u003eceramic insulator\u003c\/strong\u003e, the circuit breaks, the fuel supply cuts, and the \u003cstrong\u003eburner ignition\u003c\/strong\u003e fails. Replacing a worn electrode with this \u003cstrong\u003egenuine Viessmann part\u003c\/strong\u003e ensures your \u003cstrong\u003egas-fired boiler\u003c\/strong\u003e maintains peak \u003cstrong\u003eenergy efficiency\u003c\/strong\u003e and avoids hazardous gas accumulation. If you’re seeing intermittent faults, the \u003cstrong\u003eViessmann 7861491\u003c\/strong\u003e is the direct \u003cstrong\u003eOEM replacement\u003c\/strong\u003e for the 7839171, ensuring the exact \u003cstrong\u003etechnical specifications\u003c\/strong\u003e and mounting geometry required for a clean \u003cstrong\u003eboiler maintenance\u003c\/strong\u003e swap.\u003c\/p\u003e\n\n\u003cstrong\u003eKey Benefits for Technicians\u003c\/strong\u003e\n\u003cul\u003e\n  \u003cli\u003e\n\u003cstrong\u003eOEM Compatibility:\u003c\/strong\u003e Precision-fit for \u003cstrong\u003eViessmann CM2 boilers\u003c\/strong\u003e, acting as the primary \u003cstrong\u003eionization electrode\u003c\/strong\u003e.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eHigh-Durability Construction:\u003c\/strong\u003e Fabricated from \u003cstrong\u003eNickel Iron (NiFe)\u003c\/strong\u003e to withstand continuous exposure to high-temperature \u003cstrong\u003eflame sensing\u003c\/strong\u003e environments.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eCritical Safety Compliance:\u003c\/strong\u003e Facilitates \u003cstrong\u003eflame rectification\u003c\/strong\u003e to prevent unsafe gas flow during \u003cstrong\u003eignition failure\u003c\/strong\u003e.\u003c\/li\u003e\n  \u003cli\u003e\n\u003cstrong\u003eImproved Reliability:\u003c\/strong\u003e Reduces nuisance \u003cstrong\u003eignition lockouts\u003c\/strong\u003e and ensures consistent \u003cstrong\u003eburner signal verification\u003c\/strong\u003e.\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cstrong\u003eCommon Technician Questions\u003c\/strong\u003e\n\u003cp\u003e\u003cstrong\u003eHow do I test the Viessmann 7861491 flame sensor signal?\u003c\/strong\u003e\u003cbr\u003e\nSet your multimeter to the DC micro-amp (μA) scale. Connect the meter in series between the \u003cstrong\u003eflame sensor rod\u003c\/strong\u003e and the lead wire from the control board. A healthy \u003cstrong\u003eViessmann boiler\u003c\/strong\u003e typically requires a stable reading between 2 and 6 micro-amps; a reading below 1.7 μA usually triggers a lockout.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eWhat are the symptoms of a failing 7861491 ionization electrode?\u003c\/strong\u003e\u003cbr\u003e\nThe most common symptoms include the boiler igniting for a few seconds and then shutting down, repeated \u003cstrong\u003eignition attempts\u003c\/strong\u003e, or the \u003cstrong\u003econtrol board\u003c\/strong\u003e throwing a permanent \u003cstrong\u003eF2 or L2 fault code\u003c\/strong\u003e. Check for cracks in the porcelain insulator or heavy oxidation on the metal rod.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong\u003eCan I clean this sensor or should it be replaced?\u003c\/strong\u003e\u003cbr\u003e\nTechnicians can often remove light carbon buildup using a fine abrasive like steel wool. However, if the \u003cstrong\u003enickel-iron\u003c\/strong\u003e rod is pitted, or if the \u003cstrong\u003evoltage transmission\u003c\/strong\u003e is compromised by an internal break in the ceramic, a full replacement of the \u003cstrong\u003e7861491 flame sensor\u003c\/strong\u003e is necessary to ensure system \u003cstrong\u003eperformance\u003c\/strong\u003e.\u003c\/p\u003e\n\n\u003cp\u003e\u003cstrong style=\"color: red;\"\u003eThis item is not eligible for free shipping.\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cp\u003eDisclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.\u003c\/p\u003e","brand":"Viessmann","offers":[{"title":"Default Title","offer_id":43504624926898,"sku":"7861491","price":331.0,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1838\/2375\/files\/Pic_810961b0-30d3-4fe8-9c37-d68c47f09fd3.png?v=1752266941","url":"https:\/\/www.gsistore.com\/en-ca\/products\/viessmann-7861491","provider":"GSIstore","version":"1.0","type":"link"}