Step 3 · Verify Power is Off with a Multimeter

This is the step people usually slow down on. Go finger-tight first, then a quarter turn. No rush — replay the clip whenever it helps.

This is the most critical safety step. Set your multimeter to measure AC voltage (VAC or V~) in a range greater than 240 volts. Carefully touch the two probes of the multimeter to the top two terminal screws on the upper thermostat where the main power wires from the house connect. The multimeter must read '0' or very close to zero volts. If you get a reading of 120V or 240V, the circuit is still live. STOP IMMEDIATELY and return to the breaker panel to correctly identify and turn off the power.