If a mercury thermostat seems out of adjustment, what is the first step?

• A. Calibrate with a thermometer
• B. Inspect the capillary
• C. Replace the thermostat
• D. Check for accurate leveling

Answer: (D)

The key idea is that mercury thermostats depend on a mercury-filled capillary tube whose response must be oriented correctly. If the thermostat isn’t level, gravity shifts the mercury column, making the switch appear out of adjustment even when the sensing elements are fine. Checking and correcting leveling is the quickest, simplest way to rule out a installation-related cause before you dig into the internal sensing tube or calibration. If leveling doesn’t fix the issue, you’d then inspect the capillary for kinks, blockages, or leakage or proceed to calibration. Replacing the thermostat is considered only after leveling and basic inspections have been ruled out.