This test requires;
* A good quality digital thermometer with a bead-type thermocouple.
* A multimeter, set to test continuity - preferably using the buzzer feature.
1) Remove the two leads from the brew thermostat and connect the multimeter to the bare posts. (There are no issues of polarity, so connect them any which way.)
2) Connect the two leads removed from the tstat.
3) Attach the thermocouple to the boiler (I slip it under the thermal fuse).
4) Plug the machine in and turn it on.
5) Watch the thermometer as the temperature rises, and listen to the multimeter - it will buzz until the brew tstat opens.
6) When the multimeter stops buzzing, note the temperature reading.
The Gaggia brew thermostat is designed to open at 107C/225F. A reading of less than 100C/212F indicates a bad thermostat; replace it with a new one - or replace it altogether with a PID conversion.
Never let the thermometer reading exceed 110C/230F. If this happens, assume the tstat has failed and replace it with a new one - or replace it altogether with a PID conversion.
NOTE: This test method has some inherent risk, because it requires jumping the thermostat and wiring the heating elements directly. If you don't pay close attention to the thermometer and multimeter it is possible for the boiler to overheat to a degree that could be dangerous.
PAY CLOSE ATTENTION TO WHAT YOU'RE DOING AND DO NOT LEAVE THE MACHINE POWERED UP AND UNATTENDED FOR ANY REASON!
