How to Wire ecobee Smart Thermostat Premium With the PEK on a 2-Wire System

Overview

Older HVAC systems with only two thermostat wires need the Power Extender Kit. This guide shows how to identify terminals at the control board, wire the PEK, and finish setup in the ecobee app for stable power.

Why This Happens in Real Homes

Older HVAC systems with only two thermostat wires need the Power Extender Kit. This guide shows how to identify terminals at the control board, wire the PEK, and finish setup in the ecobee app for stable power. In day-to-day use, this usually looks like Only two wires at the thermostat; No C-wire available; ecobee powers on then reboots.

Most cases trace back to C-wire missing at thermostat; Wires not matched at control board; PEK leads swapped. The fix works best when you go step by step instead of changing multiple settings at once.

A practical order for this issue is: Shut Off HVAC Power -> Document Thermostat Wires -> Install the PEK at the Control Board -> Wire the ecobee Base. After each step, test the exact behavior that was failing so you can confirm what actually solved it.

What's Included

• Only two wires at the thermostat
• No C-wire available
• ecobee powers on then reboots
• Furnace control board accessible
• ecobee app ready for setup
• Old thermostat removed

Got your materials ready? Here's what to check first.

Before You Start

• C-wire missing at thermostat
• Wires not matched at control board
• PEK leads swapped
• Loose wire at furnace terminals
• Incorrect terminal labels
• System powered on during wiring

Tools & Requirements

Installation Steps

1

Shut Off HVAC Power

Turn off the furnace or air handler breaker. Confirm the system is off by attempting to run heating or cooling. Never wire the PEK with 24V power live.

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2

Document Thermostat Wires

Remove the old thermostat and label each wire by terminal. Take a photo of the thermostat base for reference. Keep the wires from slipping back into the wall.

3

Install the PEK at the Control Board

At the furnace control board, remove the thermostat wires from R, G, Y, and W. Insert them into the matching PEK terminals. Then connect the PEK wires to the board terminals so the system regains R, G, Y, and W.

4

Wire the ecobee Base

At the thermostat, connect the labeled wires to the ecobee terminals, including the PEK wire into the C terminal. Mount the base plate and snap on the thermostat.

5

Restore Power and Setup

Restore power and follow the ecobee app prompts. Select PEK when asked, run the equipment test, and verify heating and cooling respond correctly.

Installation Tips

Still stuck? This is usually the deeper cause below.

Need More Help? Ecobee Support

Note: The contact information below connects you directly to Ecobee's official customer support team, not Trunetto. They can help with warranty claims, device replacements, and advanced technical issues.

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