ecobee Smart Thermostat Premium / Enhanced and the Power Extender Kit: quick sheet

Covers: ecobee Smart Thermostat Premium and Enhanced (current lineup), plus older ecobee3 lite / ecobee4 that use the same Power Extender Kit (PEK). 24 V AC systems only.

Single sourceBrands: ecobee3 components

Second most common smart thermostat. ecobee needs steady power: if there is no C wire, it ships with (or uses) the Power Extender Kit, which is installed at the furnace/air handler board. Most service calls are PEK wiring errors.

Safety first

Kill HVAC power before wiring.
Not for line-voltage heaters.

How it works

The PEK converts a 4-wire (R, W, Y, G) or 3-wire (R, Y, G) cable into the signals the thermostat needs plus a common, by multiplexing at the equipment end.

The PEK works only on 24 V AC systems and is not compatible with millivolt, high-voltage, dual-transformer, fan-coil or communicating systems.

Only one PEK per system; it is rated for 24 V AC with a 2 A maximum.

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Digital thermostat mounted on a concrete wall by Alexander Mass, Pexels License

Diagnostic guides for this appliance

Guide · Thermostat

Indoor fan won't turn off from the thermostat

Start at the thermostat: fan set to ON instead of AUTO, or a setpoint the system can never reach. If the thermostat is right, the cause is in the equipment: a stuck fan relay, a limit switch keeping the blower on, a shorted G wire or a control board fault.

4 steps ~40 minmoderate

Guide · Thermostat

Thermostat shows WAIT or flashing 'Cool On'

Most thermostats hold the compressor off for a few minutes after it stops or after power returns, to prevent short cycling. That delay is normal. If the message lasts well past the delay or the system never starts, check mode, breakers, filter-related lockouts and wiring.

5 steps ~20 mineasy

Guide · Thermostat

Thermostat setpoint changes by itself

Most 'ghost' changes come from features, not faults: a program schedule resuming after a temporary hold, learning schedules, eco/away modes, utility demand-response events, or another person or app. Check the thermostat history before replacing it.

4 steps ~20 mineasy

Other thermostats manuals

Manual · Thermostat

Google Nest Learning Thermostat (3rd and 4th gen): quick sheet

Nest Learning Thermostat 3rd generation and 4th generation (released 2024). 24 V systems only.

4 components2 common failuresGoogle Nest

Manual · Thermostat

24 V HVAC thermostat control wiring: field service manual

Residential 24 VAC forced-air furnaces, air conditioners, air handlers and heat pumps (single and multi-stage). Not for line-voltage or millivolt systems.

5 components4 common failuresAll

Manual · Thermostat

Smart thermostat installation & troubleshooting: field service manual

Wi-Fi thermostats for 24 VAC systems: Nest Learning/Nest Thermostat, ecobee, Honeywell Home T-series/Lyric, Sensi, Amazon Smart Thermostat. Line-voltage models (e.g. for baseboard heat) are covered only by the safety notes.

3 components5 common failuresGoogle Nest, ecobee, Honeywell Home / Resideo, Emerson Sensi, Amazon