Upon arrival tech was informed downstairs system was thermostat was blank. Inspected system and found the air handler had 240v and 24v on board. Checked at pigtail with ezt226 and did not have 24v. Inspected safety switch and found it to be sitting slightly off and causing the plunger to raise and the thermostat to go blank. Tech adjusted switch and system came back on. System is back operational at this time.