Ul 242 [TRUSTED — 2027]

The investigation revealed that the non-UL 242 thermostat had developed a film of corrosion on its bimetal disc after just 14 months in a humid basement. That film created electrical resistance, which generated heat, which fooled the thermostat into thinking the water was hotter than it was. The heater never shut off.

In the world of safety standards, some numbers become legendary: UL 217 for smoke alarms, UL 94 for flammability. But tucked away in the appendices of electrical codes is a quieter, yet equally vital, number: UL 242 . ul 242

That is the story of UL 242: an unglamorous, forgotten, but absolutely essential standard that turns a potentially lethal appliance into a silent, trusted servant of modern life. The investigation revealed that the non-UL 242 thermostat