The Robertshaw® 110 and 220 Series gas water heater valves were first manufactured for the O.E.M. market in 1955. For the last 50 years, the 110 series has been the definitive gas water heater valve. Over the years, minor product improvements were incorporated, but the valves have remained basically the same. In 1995, Robertshaw introduced the new 220R Series gas water heater valve. The new 220R Series will mount and operate in the same manner as the original 110 Series. The 220R features simplified pilot lighting and easy-to-adjust gas pressure regulator. The 110 Series Water Heater Thermostat Uni-Kit® and Commercial Water Heater Thermostat Uni-Kits® were designed for universal replacement applications. All models feature built-in, non-cycling Energy Cut-Off (ECO) system to shut off all gas to the water heater in case of excessive water temperatures. If an ECO has detected an over-temperature condition and has opened, the control will not function and a new replacement will be required. All domestic and RV models have a 160°F temperature high stop. All commercial models have a 180°F temperature high stop. All models have a 5-1/2" sensing element and vary by inlet and outlet size, shank length, regulator type and setting. See ordering chart for exact specifications.