A lot of thermostat manufacturers tried using a "power stealing" gimmick and the gas valve coil or circuit as C and not use the C wire and it failed miserably and damaged circuit boards and caused lots of problems.
Then they came up with this add a wire electronic cheater device which was just as bad.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!