I have been working on a storage project and am finally getting close to running the entire system. I am running into a variety of Aquastat issues. Over the years I had picked up for free three single limit remote bulb aquastats, they came from a papermill and has some evidence of corrosion right out of the box. At least one looks like it doesnt work so I expected it has lost whatever working fluid/gas is used in the sensing bulb. I have worked my way around it. I figured what the heck they were free and went on to other tuning and ran into an existing aquastat with variable differential that appears to have stopped working. This Aquastat was on my wood boiler for 10 years and I dont know its prior history. In order to test out equipment, I have been moving the setting frequently so it has been getting a lot of use. All indications are that the electrical contacts are fine, its just that the bulb assembly is no longer responding to temperature. I will probably order a new one, but was curious, have other experienced failure of previously reliable aquastats after making a lot of adjustments? The other question is has anyone ever tried to fix one?