Why Won't My Vivint Smart Thermostat Heat?
- Set to Cool or Off instead of Heat
- Setpoint not above the current room temperature
- Furnace not igniting (dirty flame sensor, no fuel, tripped limit)
Problem Description
Your Vivint smart thermostat is not turning on the heat when expected. The most common cause is the thermostat being set to Cool or Off mode instead of Heat. The set temperature must also be above the current room temperature for the heat to kick on. This guide covers checking the mode, verifying the setpoint, and checking HVAC system status.
Why This Happens in Real Homes
Most 'Vivint thermostat won't heat' cases are simpler than they look, so start with the settings on the thermostat itself. It has to be in Heat mode, and the setpoint has to be above the current room temperature for a heat call to begin - it's easy to leave it on Cool or Off, or to set a target below the current temp. A related giveaway is the fan: if it's set to ON it runs continuously and blows room-temperature air between heating cycles, which feels like 'blowing cold,' whereas AUTO runs the fan only when the system is actually heating.
If the settings are right and there's still no heat, the problem is usually in the furnace or the connection rather than the thermostat. Common furnace culprits are a dirty flame sensor (which shuts the burner down as a safety), a tripped breaker, an open furnace door safety switch, no fuel, or a clogged filter tripping the high-limit switch - so check the HVAC system itself. On the connectivity side, the Vivint thermostat talks to the panel over Z-Wave and needs steady C-wire power; a missing C-wire causes it to lose power and reboot, and a dropped Z-Wave link leaves it offline and unresponsive. Rebooting the panel restores the link, and if the screen is going blank, the C-wire is the thing to fix.
Symptoms
- Heat won't turn on when expected
- Set to Heat but no warm air
- Displays temperature but heat never starts
- Heating worked before, then stopped
- Thermostat offline or unresponsive
- Fan runs but blows cold air
- Aux/emergency heat not engaging
- Setpoint above room temp but no heat
Recognize these? Here's what usually causes it.
Common Causes
- Set to Cool or Off instead of Heat
- Setpoint not above the current room temperature
- Furnace not igniting (dirty flame sensor, no fuel, tripped limit)
- Fan set to ON circulating unheated air
- Missing C-wire causing power loss/reboot
- Lost Z-Wave connection to the panel
- Tripped HVAC breaker or open furnace safety switch
- Clogged filter tripping a high-limit shutoff
Most fixes happen in the first 3 steps.
Always turn off your HVAC system at the breaker before removing the thermostat or touching wires. Incorrect wiring can damage both the thermostat and your HVAC equipment resulting in expensive repairs. If unsure about wiring consult an HVAC technician.
Tools & Requirements
Step-by-Step Solution
Verify the thermostat is set to Heat mode
On the Vivint thermostat or in the Vivint app, check the system mode. It should be set to Heat (not Cool, Auto, or Off). If set to Cool, the system calls for cooling, not heating. If set to Off, the HVAC does not run at all. Also check that the set temperature is above the current room temperature — the thermostat only calls for heat when the room temperature drops below the setpoint.
Check the furnace or heat source
Go to your furnace or heat pump. Is it running? Listen for the blower fan and burner ignition. If the furnace is completely silent: check the power switch on the furnace (looks like a light switch on the side of the unit — it must be on). Check the breaker in your electrical panel. If the furnace fan runs but no hot air comes out: the igniter or gas valve may have failed — this requires HVAC service, not a thermostat fix.
Check the air filter
A severely clogged air filter restricts airflow, causing the furnace to overheat and trigger the high-limit safety switch. When the safety trips, the furnace shuts down and the thermostat shows it is calling for heat but nothing happens. Pull out the air filter and inspect — if you cannot see light through it, replace it. After replacing the filter, wait 10 minutes for the high-limit switch to reset, then the furnace should restart.
Check wiring at the thermostat
If the thermostat calls for heat (the Vivint app shows Heating) but the furnace does not respond: the W (heat) wire may be loose at the thermostat. Remove the thermostat cover and check the wiring terminals. The W wire (usually white) must be firmly connected to the W terminal. Also check the R wire (red, 24V power) — if the R wire is loose, the thermostat has no control signal to send.
Bypass the thermostat to test the furnace
If you suspect the thermostat is the problem: turn off HVAC power at the breaker. At the thermostat base plate, take the R wire and touch it to the W wire momentarily (this simulates the thermostat calling for heat). Turn the breaker back on. If the furnace ignites, the thermostat or its Z-Wave communication is the issue. If the furnace still does not ignite, the problem is in the furnace, not the thermostat. Call an HVAC technician for furnace repair.
Quick Solutions
Still having issues? This is usually the deeper cause below.
Schedules that skip randomly are usually a daylight-saving holdover — delete and recreate the schedule to clear the corrupted entry.
Use the thermostat energy reports to find patterns in your heating and cooling usage. Setting back the temperature just 3 degrees when you leave for work can save 5 to 10 percent on your annual energy bill without any comfort sacrifice.
Thermostat issues that keep returning are often caused by stale backup-battery memory holding old settings across power cycles without the user realising.
- Set to Cool or Off instead of Heat
- Setpoint not above the current room temperature
- Furnace not igniting (dirty flame sensor, no fuel, tripped
- Fan set to ON circulating unheated air
- Missing C-wire causing power loss/reboot
Before you go — try one of these (they fix most cases).
Official Manufacturer Manual
Vivint provides official product documentation through their online manual rather than downloadable PDF. Access setup guides, troubleshooting steps, and product specifications for your Vivint Element Thermostat.
Source: support.vivint.com
Need More Help? Vivint Support
Note: The contact information below connects you directly to Vivint's official customer support team, not Trunetto. They can help with warranty claims, device replacements, and advanced technical issues.