Vent, Valve & Volt
Vent: HVAC

Thermostat screen is blank

A blank thermostat usually means it has lost power: dead batteries, a tripped breaker, the furnace door switch, or a float switch that shut the system down. These questions walk through each one, in the order Honeywell lists them.

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A homeowner frowning at a wall thermostat with a blank screen
A thermostat on the wall with two possible power sources: batteries inside it, or a common wire from the furnace or air handler, which is fed by the furnace power switch and a breaker. blankbatteries (some models) C wire furnace orair handlerswitch breaker a loose furnace door, a tripped breaker or a float switch can cut the C wire's power
Where thermostats get their power
Every question and answer on this page, in order

Question 1: Does your thermostat take batteries?

Battery models usually have a door on the side or bottom, or the face pulls off to show AA or AAA batteries.

Question 2: Put in fresh batteries. Is the screen back?

Use fresh alkaline batteries of the same brand, and match the + and - marks.

Question 3: At the furnace or air handler, check the power switch, the front door panel and its breaker. What do you find?

Look only; don't remove panels. The power switch often looks like a light switch on or near the unit.

Question 4: Reset the breaker once, firmly off then on. Did it hold?

Open only the hinged panel door, never the metal cover behind it.

Question 5: Is there water in the drain pan or on the floor around the indoor unit?

A float switch in the drain pan can cut power to the whole system, thermostat included.

Question 6: Is the thermostat's face sitting flush on its wall base?

Many thermostats pull straight off a wall plate. Look for a gap along one edge.

Possible results

Need the words for the phone call? Build a what-to-tell-the-technician checklist, or read when to call an hvac pro.