Looks like a low return temperature sensor for a boiler type heating appliance. L49-10 indicates it's open at 49 deg. and closes with a 10 deg rise. This would limit the return water/fluid temp, anything above the limit setting allows flow through the appliance, below the limit recirculates within the appliance.
2019 Winnebago Forza 36G
2018 Jeep Wrangler Sahara
Anchorage Alaska when not on the road