I’m Nathan, and I’ve worked as an HVAC technician for over 10 years. When someone tells me, “My Ecobee is on, but the house is cold,” the issue is almost always one of three things:
- The thermostat is not actually calling for heat because of a setting or threshold
- The thermostat is calling, but the furnace or heat pump is not responding due to a safety lockout or power issue
- The equipment is trying to heat, but it shuts down because of airflow or ignition problems
In this guide, I’ll walk you through the same checks I do in the field, in the right order, so you don’t waste time.
Before You Start: Safety and What You’ll Need
If you plan to open your furnace panel or touch wiring, turn off power at the furnace switch or breaker first.
Helpful tools:
- Flashlight
- New air filter (correct size)
- Small screwdriver
- Phone camera (take a picture of wiring before you move anything)
- Optional: multimeter (if you’re comfortable using one)
2 Minute Quick Check (Do This First)
These quick checks solve a surprising number of “Ecobee not heating” calls.
- On the Ecobee, confirm System Mode = Heat (or Auto)
- Raise the set temperature at least 2 to 3 degrees above room temp
- Look for the flame icon and “Heating” status
- Make sure you are not in a schedule setback or vacation/away comfort setting
- Check your furnace switch (looks like a light switch) and the breaker
If you do those and still no heat, continue below.
Common Reasons an Ecobee Is Not Heating (With Fixes)
| No power to furnace or air handler | Ecobee may be blank, or heat never starts | Check breaker, furnace switch, door switch |
| Thermostat settings or thresholds | Ecobee looks normal but won’t start heat | Verify mode, setpoint, thresholds, heat pump settings |
| Reversing valve O B set wrong (heat pump) | It blows cool air when set to heat | Change O B orientation in Ecobee settings |
| Furnace overheating (limit switch trips) | Heat starts then shuts off, repeats | Replace filter, open vents, check blower and airflow |
| Ecobee not getting consistent power (C wire / PEK issues) | Clicking, short cycling, heat doesn’t fully start | Install PEK, fix C wire, test with R to W jumper |
| Furnace fails ignition or trips safeties | No flame, error code blinking | Read error code, check igniter, gas, pressure switch |
| Defective thermostat (rare) | Everything else checks out | Confirm with jumper test, then replace thermostat |
Step 1: Confirm the Ecobee Is Actually Calling for Heat
Even if the screen says “Heat,” the thermostat may not be calling for a heating cycle yet.
What I check on the Ecobee
- System Mode: Heat
- Fan: Auto (for most systems)
- Set temperature: at least 2 to 3 degrees above current room temp
- Equipment running status: Look for “Heat” or “Stage 1 Heat” in the running equipment screen
Step 2: Check Power to the Furnace (Most Missed Step)
In real service calls, I see “thermostat problems” that are actually furnace power problems all the time.
Check these in order
- Breaker: HVAC, furnace, air handler, or “heat” breaker tripped
- Furnace service switch: near the furnace, looks like a light switch
- Furnace door switch: if the panel is not seated correctly, the furnace won’t run
- Condensate float switch (common on high efficiency furnaces): if the drain is clogged, it can shut heat off
Step 3: Ecobee Settings That Commonly Stop Heat
3A. Make sure your equipment type is correct
If you have a heat pump and the thermostat is configured like a gas furnace (or vice versa), it can behave weirdly.
On Ecobee go to:
Settings → Installation Settings → Equipment
Confirm whether you have:
- Heat pump
- Furnace (gas or electric)
- Dual fuel (heat pump with furnace backup)
3B. Heat pump problem: O B reversing valve set wrong
This is a classic one. If your system cools when it should heat, or heats when it should cool, the reversing valve setting is likely backwards.
Go to:
Settings → Installation Settings → Equipment → Heat Pump → O B Reversing Valve
Try switching the orientation:
- Energized on Cool
- Energized on Heat
In the field, this fix is extremely common after a new thermostat install.
3C. Use Test Equipment to force heat on
Ecobee has a built in way to test each stage.
Go to:
Settings → Installation Settings → Test Equipment
Then test:
- Heat stage 1
- Heat stage 2
- Aux heat (if you have it)
If Test Equipment turns heat on, your issue is usually configuration, thresholds, or scheduling, not a broken furnace.
Step 4: Overheating Furnace (Dirty Filter Is the Big One)
Furnaces have safety switches, especially a high limit switch, that shut the burners off if the unit is getting too hot. Most homeowners don’t realize the furnace is protecting itself.
Signs of overheating and limit trips
- Heat starts for 2 to 5 minutes then shuts off
- Fan keeps running
- It repeats in short cycles
- The house never warms up
What to do
- Replace the air filter with the correct size and airflow rating
- Make sure supply vents are open and not blocked
- Make sure return grilles are not blocked (this matters a lot)
From my experience, airflow problems are one of the top causes of short cycling in heating season. A filter that is heavily loaded can restrict airflow enough to trigger high limit shutdowns.
If you replace the filter and it still trips, you may have a blower issue, dirty evaporator coil, or a plugged heat exchanger path. That is a professional service call.
Step 5: Furnace Will Not Ignite (Thermostat May Be Fine)
If the Ecobee is calling for heat but the furnace won’t light, the thermostat is not the main problem.
What I do at the furnace
Most furnaces have a small viewing window and a control board with an LED light.
- Call for heat at the thermostat
- Watch the furnace sequence:
- Inducer motor starts
- Igniter glows or sparks
- Gas valve opens
- Flame lights
- Blower starts
Check the error code
Look for a blinking LED on the furnace control board and match it to the chart on the furnace door.
Common causes:
- Dirty flame sensor
- Failed igniter
- Pressure switch issues (venting or condensate related)
- Gas supply or gas valve issue
- High limit open from overheating
If you see repeated ignition attempts with no flame, or you smell gas, stop and call a pro.
Step 6: Ecobee Not Getting Consistent Power (C Wire and PEK Issues)
Ecobee thermostats need steady power. If the power steals through other circuits or the C wire is missing or weak, you can get strange behavior like heat not starting reliably.
A quick field test (if you’re comfortable)
Turn off power, pull the Ecobee off the wall, then look at the wiring.
If you temporarily jumper R to W1 at the thermostat base and the furnace runs, that tells me:
- The furnace and wiring can respond to a heat call
- The issue is likely thermostat power, configuration, or thermostat itself
The PEK solution
If you don’t have a dedicated C wire, Ecobee includes a PEK (Power Extender Kit) for many systems. Installing it at the furnace control board often fixes:
- Random shutoffs
- No heat calls reaching the furnace
- Thermostat rebooting
Important note from what I’ve seen: even some homes that technically have a C wire still have voltage drop or wiring issues that cause symptoms similar to “no C.” Fixing the C circuit properly or using the PEK can stabilize things.
If you’re not comfortable wiring at the furnace board, this is a good time to call an HVAC tech. It is usually a quick service visit.
Step 7: Wiring Mistakes That Stop Heat
If your Ecobee was recently installed or moved, wiring is high on the suspect list.
Common wiring issues I run into:
- W1 not seated fully in the terminal
- W wire landed on the wrong terminal
- Heat pump wires mixed up (O B, AUX, W1)
- Rc and Rh confusion (Ecobee typically handles this internally, depending on model and setup)
Ecobee Not Turning On Aux Heat (How I Fix It)
Aux heat can mean electric heat strips or a furnace backup, depending on your system. Ecobee usually controls aux heat using thresholds, not just demand.
Step 1: Confirm Aux heat works in Test Equipment
Go to:
Settings → Installation Settings → Test Equipment → Aux Heat
If Aux heat turns on in test mode, your wiring is likely fine and the problem is thresholds or lockouts.
Step 2: Understand the settings that block Aux heat
Go to:
Settings → Installation Settings → Thresholds
The exact names vary a bit by model and setup, but these are the big ones:
| Compressor minimum outdoor temperature | Locks out heat pump below a certain outdoor temp | Heat pump may stop, aux may not take over correctly if configured wrong |
| Aux heat minimum outdoor temperature or lockout | Prevents aux from running above or below certain temps | Aux never turns on when you expect it |
| Compressor to Aux temperature delta | How far behind the room temp can fall before aux engages | If too high, your home may feel cold before aux helps |
| Simultaneous Aux Heat | Allows aux to run with heat pump | If disabled, aux may feel delayed in very cold weather |
Step 3: Make sure you’re using the right mode
On Ecobee:
- Heat mode means it will decide between heat pump and aux based on thresholds
- Aux mode typically means aux only, no heat pump
If you accidentally expect aux to run while you’re in a mode that prevents it, it will look like aux is “broken” when it’s actually following settings.
Step 4: Outdoor temperature data matters
If your Ecobee is using internet weather and it’s wrong, thresholds can behave wrong. If you have an outdoor sensor, even better, but it must be configured correctly.
Symptom Checker (Fast Diagnosis)
| Ecobee screen is blank | Furnace power off, breaker, blown fuse, C wire issue |
| Ecobee says “Heating” but no furnace activity | Furnace safety lockout, broken W circuit, control board issue |
| It heats for a few minutes then stops | Overheating, dirty filter, limit switch opening |
| Blowing cold air in Heat mode (heat pump) | O B reversing valve setting wrong |
| Aux never turns on even when cold | Thresholds, lockouts, aux wiring or configuration |
| Heat works in Test Equipment but not normally | Schedule, comfort settings, thresholds, staging settings |
When You Should Call a Pro
I’m all for DIY checks, but call for service if:
- Breaker trips repeatedly
- Furnace shows persistent error codes you can’t clear
- You smell gas or suspect a gas issue
- The furnace ignites with a bang or you see flame rollout
- You replaced the filter and it still short cycles on high limit
In many cases, a no heat service call ends up being a simple repair like a flame sensor cleaning, a condensate drain clearing, or correcting a wiring/config issue.
Maintenance Tips That Prevent This Problem
What I recommend to homeowners I work with:
- Change filters regularly (most homes every 1 to 3 months depending on filter type and dust)
- Keep return grilles open and unblocked
- Have your system serviced at least once a year (twice a year if you want heating and cooling checked separately)
- If you have a high efficiency furnace, keep the condensate drain line clear
Final Thoughts
If your Ecobee thermostat is not heating, don’t assume the thermostat is bad. Most of the time it’s power, thresholds, a heat pump reversing valve setting, airflow causing furnace limit trips, or the furnace failing ignition due to a safety condition.
