Field Controls 46086900 WMO-1 Blocked Vent Thermal Safety Switch

The Field Controls 46086900 WMO-1 is a thermal safety switch designed to protect oil-fired furnaces, boilers, and water heaters from hazardous flue gas spillage conditions. This critical safety device detects blocked vents, continuous downdrafting, or inadequate draft conditions by monitoring heat buildup from escaping flue gases.

Key Features:

• 120 volt, 10 amp SPST (single pole, single throw) switch configuration
• Opens at 200°F to shut down burner operation when excessive heat is detected
• Manual reset operation prevents automatic restart until the problem is resolved and the switch is manually reset
• Silver contacts for reliable electrical performance
• Designed for installation on barometric draft controls and draft hoods

How It Works:

When wired in series with the burner circuit, the WMO-1 continuously monitors for hot flue gases backing up through its heat transfer tube. If the switch detects spillage due to a blocked vent or draft problem, it de-energizes the burner or burner control to prevent carbon monoxide buildup and other dangerous conditions. The switch must be manually reset after the underlying ventilation problem has been corrected, ensuring safe operation before the system can restart.

This safety switch is an essential secondary safety device for oil-fired heating equipment, providing reliable protection against unsafe venting conditions that could endanger occupants.