My (Carrier) thermostat was on E3 when I returned from work this afternoon (6 p.m.)
I reset breakers for heat pump and for furnace, changed filter and then my son opened the back of the thermostat - closed it back up.
Now the thermostat screen is blank and there is no airconditioning, no fan.
It is a duel fuel system.
What is wrong and what else should I try before calling in a repair service call?

Are batteries good? And in place? Check back of stat to see if push pins are bent.

are batteries good? and in place? check back of stat to see if push pins are bent.

No battery - direct wired. Push pins are in fine condition. First message was actually E2 - not E3. Carrier site stated E2 meant "brown out conditions" However all other power in house seems OK

Is the fuse at furnace OK?

There are 2 one on side of furnace for main power, and maybe one in bottom door 3 amp car fuse on the control board

there are 2 one on side of furnace for main power, and maybe one in bottom door 3 amp car fuse on the control board
In attic now - - - searching. It is a gas furnace. 9200 Weathermaker. Popped off panel - lots to read - but no sign of a fuse. We did have storms last night - lightning and power flashes - but no all out outage. Storms in previous two weeks blue fuse from transformer for main house power 3 times in one day - 3 other days as well. Is it possible thermostat was damaged?

Could have been or blown transformer. Did you find control panel? Is there a fuse or lights on it? If so look to see if the little light comes on when you press the door swithc in.

could have been or blown transformer. did you find control panel? is there a fuse or lights on it? if so look to see if the little light comes on when you press the door swithc in.

No... didn't find correct panel to remove on the furnace and no visible control panel doors.(and am darned frustrated and feeling incompetent by that) Large panel I removed did house connections, wires, exhaust for the gas... No switches. No fuses.

With all other actions taken - feel strongly you are 100% right about fuse. Just can't find access to a control panel on the furnace.

Thank you for your attempts to help out. Working now on finding a place for my mother to spend the day tomorrow and notifying my supervisor of time needed off from work until a service call can be placed and made. We are lucky to have a surprisingly cooler evening this July night... things will heat up again with the coming of sunrise, tomorrow.

Furnaces have 2 doors the control panel should be in the one opposite from where the vent comes out, may have a metal cover over it after taking door off

furnaces have 2 doors the control panel should be in the one opposite from where the vent comes out, may have a metal cover over it after taking door off

OK - service call complete. I now see where the metal cover was that you referred to. Problem was no power in neutral wire... Search was on. Located fried wires in switch/junction box mounted on post next to furnace. Never dawned on me to check there because pull chain attic light also runs from the same switch box and was operational. Wires fried were leading out of box to the furnace.