Why is my Nest thermostat screen blank?

Google's support flow: the display may not be receiving HVAC power, or the internal battery drained because the system isn't charging it. Reseat the display, confirm the breaker and furnace switch, then charge via USB or replace batteries as your model allows. Persistent no-power alerts (E298/E448/M20) point to wiring or a missing C wire, Nest Power Connector, or similar power path.

Why is my ecobee screen black?

ecobee thermostats need continuous 24 VAC from the HVAC — they don't run on a replaceable display battery for normal use. Check breaker, closed equipment door, control-board fuse, and firm Rc or R wire and C wire on the Rc or R terminal and the C terminal. No C wire often means installing the ecobee PEK or landing a spare on the C terminal.

Should I jump the condensate float switch to wake the thermostat?

No. A tripped float is a flood/overflow safety. Clear the drain and pan; jumping the switch risks water damage and mold. Call a tech if the float or drain pan needs service.

Thermostat blank screen / no power

By Dan Mercer · Published October 5, 2026 · Updated October 6, 2026 · Sources

Blank thermostat screen — heat/cool won’t call

A dark Nest or ecobee usually means the display isn’t getting enough 24 V power from the HVAC — drained battery (Nest), missing or loose C wire on the C terminal, open furnace door switch, tripped breaker, or a blown control-board fuse. Calm checks first. DIY at your own risk; line-voltage and gas-furnace work are stop lines. Skip Infinity / ComfortLink communicating-control dumps — those are installer literature.

Part of Thermostats & HVAC controls — wall controls, not washer/dryer error codes.

Read this before any DIY — stop lines

DIY at your own risk. General guidance only. Follow Google Nest / ecobee support articles and your furnace/air-handler manual.
Kill HVAC power at the breaker or furnace switch before pulling the thermostat off the wall or touching control-board terminals.
Line voltage (120/240 V) at the equipment is electrician / HVAC tech territory — thermostat terminals are low-voltage, but the furnace cabinet is not a toy.
Gas smell: leave the building; call the gas company. No DIY on gas valves or burners.
No Infinity / ComfortLink / communicating zone-board dumps on this page — if your system uses a proprietary communicating thermostat, use the OEM app/dealer path.
Mold / condensate: a float switch that cuts 24 V can blank a smart thermostat when a drain pan is full — fix the water problem; don’t bypass safety switches.

How to restore power to a blank Nest or ecobee

Work top to bottom. Power off before reseating wires. DIY at your own risk.

Check the HVAC breaker and furnace switch. Confirm the HVAC breaker is on. Many furnaces have a light-switch-style service switch nearby — it must be ON.
Close the furnace or air-handler door switch. The panel door switch must be fully closed; an open door kills control power and looks like a dead thermostat.
Reseat the Nest or ecobee display on its base. Pull the display straight off the base and push it firmly back on until it latches.
Wait for Nest to recharge after an outage. Nest may need time to recharge its internal battery from the system once power returns.
Seat the Rc or R wire and the C wire on the thermostat. Confirm the Rc (or R) wire is firmly seated on the Rc (or R) terminal and the C wire is firmly seated on the C terminal.
Optional meter check between the R (or Rc) terminal and the C terminal. With power on and only if you are comfortable metering, measure about 24–29 VAC between the R (or Rc) terminal and the C terminal.
Stop line: do not jump a condensate float switch. Do not jump a condensate float switch to wake the thermostat; clear the drain path or call a pro.

Terminal tokens used on this page

Uppercase standalone letters for snippets, each named as its own terminal:

R — 24 VAC hot (single-transformer bases)
Rc — 24 VAC hot for cooling transformer
Rh — 24 VAC hot for heating transformer
C — 24 VAC common (continuous return)
Y — cool call / compressor
W — heat call
G — fan call

Google Nest — blank or won’t turn on

Google’s help article Troubleshoot when your thermostat won’t turn on covers a dark, unresponsive Nest:

Pull the display; if the baseplate level indicator doesn’t light, the thermostat isn’t receiving system power on the R terminal and the C terminal.
Cycle the HVAC breaker/switch fully off and on; check fuses if you have a fuse box.
Drained battery often means the system isn’t delivering enough power over the thermostat wires — USB charge (Learning models) or AAA batteries (Thermostat E), then remount.
If it wakes with a “No power” / “No system power” alert or help codes such as E298, E448, or M20, follow Google’s dedicated no-power article: Settings → Equipment → wiring info; grey (no voltage) on a terminal in Nest wiring info means that terminal is not energized; power off before reseating wires on the R, C, Y, W, and G terminals.

Verify for your Nest model — Learning, E, and newer Nest Thermostat generations differ on battery vs USB recovery. Dedicated Nest guides will land on the Thermostats & HVAC controls hub.

ecobee — black screen / won’t turn on

ecobee’s power troubleshooting notes that the thermostat has no internal battery power source for normal operation — it needs 24 VAC from the HVAC:

Confirm the Rc (or R) wire and the C wire are firmly seated at the thermostat.
Breaker on; equipment door closed; check the furnace control-board fuse (often 3–5 A) per your HVAC manual.
If you can safely meter: about 24–29 VAC between the R (or Rc) terminal and the C terminal (power on, meter-comfortable homeowners only).
Clicking without a boot often means weak voltage between the Rc terminal and the C terminal — a bad or loose C wire, or an ecobee PEK wiring issue.

Dedicated ecobee guides will land on the Thermostats & HVAC controls hub.

C terminal, Nest Power Connector, ecobee PEK

The C terminal (common) provides continuous 24 V. Heat-only, cool-only, zone, and some heat-pump setups often need a C wire on the C terminal.
Nest: an unused conductor can become the C wire if landed on the C terminal at the control board; otherwise use a Nest Power Connector (Google’s C-wire article).
ecobee: Power Extender Kit (ecobee PEK) at the control board when you lack a C wire — not for every dual-transformer / heat-only layout; follow the app diagrams. The ecobee PEK installs inside the equipment — if you’re not comfortable, hire a tech.
If the base has both the Rc terminal and the Rh terminal, land power per the OEM jumper rules; land common on the C terminal. Never guess dual-transformer wiring.
Never bypass a condensate float switch or high-limit just to wake the thermostat.

When to call a pro (clear stop)

You smell gas, see scorched wires, or the control-board fuse keeps blowing.
You’re not comfortable opening the furnace/air-handler or landing a C wire, ecobee PEK, or Nest Power Connector.
Zone panels, dual transformers, or communicating OEM thermostats (Infinity, ComfortLink, etc.).
Blank screen plus no heat/cool and equipment never starts — could be a failed transformer or control board.
Water in the secondary drain pan / float open — fix drainage; don’t jump the float.

Thermostats & HVAC controls · AC & heat pump codes · Dehumidifier codes · Humidifier · All appliances

Sources

Google Nest Help – Troubleshoot when your thermostat won’t turn on: support.google.com/googlehome/answer/9233319
Google Nest Help – “No power” alert (E298, E448, M20): support.google.com/googlenest/answer/10191637
Google Nest Help – Common / C wire & Power Connector: support.google.com/googlenest/answer/9251212
ecobee Support – Thermostat won’t turn on / power troubleshooting: support.ecobee.com (power issues)
ecobee Support – Power Extender Kit (no C wire): support.ecobee.com (PEK)

Drafted with AI assistance and checked against the public manufacturer support pages above. DIY steps are optional and at your own risk. Not a substitute for a licensed HVAC technician, electrician, or Nest/ecobee support. No Infinity/ComfortLink code dumps on this page.