In sealed combustion systems

the internal bimetal disc may be defective

It is commonly used in water and fluid systems to protect pumps and downstream components from over-pressurization

including those by Allied

frequently utilized for freeze protection or low-ambient cooling cycles

Ranco O16-120 Pressure Control 30067439-890 In sealed combustion systemsThe Ranco O16 120 is a heavy duty single low pressure control designed for precise regulation in commercial refrigeration and HVAC systems. Built with a SPDT switch (Single Pole Double Throw), this control provides professional grade flexibility by allowing for either opens on low pressure or opens on high pressure wiring configurations, making it compatible with a wide range of compressors and fan cycles. It features a broad pressure range of 12" WC