{"product_id":"mcdonnell-miller-129502-42s-hd-head-mechanism","title":"McDonnell \u0026 Miller 129502 42S-HD Head Mechanism","description":"\u003cp\u003eEnsure reliable boiler safety and precise water level control by replacing worn internal components with the \u003cb\u003eMcDonnell \u0026amp; Miller 129502 42S-HD Head Mechanism\u003c\/b\u003e. Engineered specifically to restore the operational integrity of \u003cb\u003e42S\u003c\/b\u003e and \u003cb\u003e42S-A\u003c\/b\u003e series low water cut-offs, this head mechanism serves as a direct fit replacement to maintain your system's regulatory compliance and safety standards.\u003c\/p\u003e\u003cp\u003eThis head assembly houses the critical switching components that detect boiler water levels, converting mechanical float movement into precise electrical control signals. By installing this factory-authorized replacement, you resolve common fatigue issues associated with aging sensors, ensuring consistent burner cut-off performance and protection against dry firing.\u003c\/p\u003e\u003ch4\u003eKey System Performance Baselines:\u003c\/h4\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cb\u003ePrecision Control:\u003c\/b\u003e Engineered for reliable, repeatable water level sensing in hydronic applications.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eDurability:\u003c\/b\u003e Constructed from industrial-grade materials to withstand the high-temperature, high-pressure demands of boiler rooms.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eCompatibility:\u003c\/b\u003e Designed for seamless integration with 42S and 42S-A series McDonnell \u0026amp; Miller units.\u003c\/li\u003e\n\u003cli\u003e\n\u003cb\u003eOperational Efficiency:\u003c\/b\u003e Restores factory-specified response times for critical low-water safety shutdown.\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003e⚠️ \u003cstrong\u003eApplication Profile:\u003c\/strong\u003e Recommended for use in commercial and residential steam boiler systems, low water cut-off maintenance, and preventative boiler safety upgrades.\u003c\/p\u003e","brand":"McDonnell \u0026 Miller","offers":[{"title":"Default Title","offer_id":43124937523294,"sku":"129502","price":1128.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0663\/7151\/8558\/files\/129502_image_50409607-bdf5-4e99-b433-cff9a6fd0742.png?v=1786035469","url":"https:\/\/nationalboilersupply.com\/products\/mcdonnell-miller-129502-42s-hd-head-mechanism","provider":"National Boiler Supply","version":"1.0","type":"link"}