How To Test Honeywell Water Heater Thermostat. To test a water heater thermostat, start by turning off power at the breaker then remove cover plates and insulation. Then, using the second probe, contact each one of the thermostat connections and the connectors of both heating elements.

The first thing you need to do before you attempt any work on your water heater is, turn the power off. Once the power is off, use a screwdriver to remove the thermostat’s cover. It could be tripped for several reasons.