Ecobee Keeps Saying “Calibrating” or Rebooting? It Is Losing Power

The Short Answer

An ecobee has no battery. It runs entirely on 24 V from your heating and cooling equipment, so when that power drops, the thermostat goes black, restarts and shows “Calibrating” while it comes back up. ecobee’s support article on rebooting says exactly this: if the thermostat frequently loses power or is displaying a “calibrating” message, the job is to find what is cutting the power.

A single “Calibrating” after installation or a power cut is normal. Seeing it again and again — especially just after the heat or air conditioning kicks in — is the symptom this guide is about.

Step 1: Confirm It Is a Power Loss (System Monitor)

ecobee suggests using the System Monitor in the app or web portal. Power losses show up as gaps in the runtime data. Look at what happened just before each gap:

• A heating call right before the gap (or the house is warmer when data resumes) → the power drops during heating.
• A cooling call right before the gap (or the house is cooler when data resumes) → the power drops during cooling.

That tells you which half of the checklist below to use.

If It Reboots During Heating

Furnace overheating. When a furnace overheats, its built-in safety switch (the high-limit) cuts heat or power to protect it, and the blower may keep running to cool it down. Once it has cooled, the furnace and the ecobee come back on — which looks exactly like a random reboot. ecobee lists the common causes:

• Reduced airflow: a clogged filter, or a blocked air intake outside. Replace the filter first; it is the cheapest check there is.
• Dirt and carbon build-up: if a fresh filter does not stop it, have the furnace serviced and cleaned.
• Very long runs: in severe cold, large setpoint jumps keep the furnace running flat out. Smaller steps in your schedule help.

Boilers and zone valves. Many boiler and zone-valve systems, especially older ones, do not have a transformer big enough to power one or more smart thermostats. ecobee says most boiler systems need a separate 24 V, 40 VA transformer for the ecobee, and so does a zone-valve system with more than three zones.

If It Reboots During Cooling

A blocked condensate drain. An air conditioner pulls water out of the air, which drips into a pan and drains away. If the drain line clogs, the pan fills and a float switch (or condensate pump) cuts power to the system to prevent water damage. When the water drains, power — and your ecobee — comes back. Clear the condensate line so water flows freely.

Overheating. As with heating, a clogged filter can make the system overheat and trip. Replace or clean it.

If It Has Never Had a C Wire

If the reboots started right after you installed the ecobee, check how it is powered. Most ecobee models need a C (common) wire. ecobee’s Power Extender Kit is its solution for homes without one; it is included with the Premium and sold separately for the Essential.

For the general version of this problem on any brand, see smart thermostat black or blank screen.

When to Call a Technician

ecobee’s own advice is to consult your HVAC manual or a contractor if the problem persists. Call one if a furnace keeps tripping its high-limit with a clean filter, if the float switch keeps tripping after you clear the drain, or if you would need to add a transformer. These involve the line-voltage side of the equipment.

Frequently Asked Questions

Why does my ecobee keep saying Calibrating?

Because it keeps restarting. An ecobee has no internal power source, so any interruption to its 24 V supply makes it reboot and show Calibrating while it starts up. Find what is cutting the power, usually during heating or cooling.

How long should an ecobee calibrate?

A short calibration after installation or a power cut is normal. If it keeps coming back, the thermostat is losing power repeatedly.

Can a clogged AC drain make my ecobee reboot?

Yes. A full drain pan trips the float switch, which cuts power to the system and therefore to the thermostat. Clearing the condensate line fixes it.

Does an ecobee need a C wire?

Most models do. The Power Extender Kit is ecobee’s alternative for homes without one; it comes with the Premium and is sold separately for the Essential.

Related Guides

• Ecobee offline or keeps going offline — when the screen works but Wi-Fi does not
• Smart thermostat black or blank screen — the full power-path checklist
• Smart thermostat troubleshooting — every fix guide by symptom

Sources

• ecobee Support: Why is my ecobee thermostat rebooting?
• ecobee: Power Extender Kit