Sensi Thermostat Blowing Cold Air On Heat [Fixed]

Is your Sensi  thermostat blowing cold air on heat? If so, then this is a perfect guide for you!

There are a several things can could prevent your Sensi thermostat from heating and we are going to the looking at the most common ones in this guide

Generally  when your Sensi thermostat is blowing cold  air in heat mode, this could be due to incorrect thermostat settings, stuck reverse valve,  wrong thermostat wiring,ignition failure, clogged condensate lines and a few more others we shall be looking at this guide.

Possible reasons your Sensi is blowing cold air on heat

Possible causefix
Sensi set to fan  ‘on’Put the fan setting to auto
Heat pump reverse valve stuck on coolSet thermostat to heat, if you have a heat pump
Wong thermostat wiringCheck wiring and wire it correctly
Ignition failureCheck furnace
Dirty flame sensorclean/ replace   flame sensor
Damaged ductworkSeal off leaky ductwork
Possible causes and fixes

1) Incorrect thermostat setting

One of the commonest reasons a Sensi thermostat could blow cold air on heat mode is because the thermostat fan setting is set to ‘ON’ instead of auto or heat. When the fan is ‘ON’, the air handler  fan will continue blowing air even when the thermostat is in the down cycle. This causes the air blowing out of the vents to feel cold.

Another possibility is that you might have forgotten to switch between heating and cooling


Check your thermostat to ensure that it has the correct thermostat settings. Look at the fan setting, it should be set to auto or heat. But if it’s set to ‘ON’ adjust it accordingly.

Also read: Honeywell thermostat blowing cold air on heat

2) Stuck Reversing Valve

This applies to homeowners that use a heat pump

A stuck reverse valve is another possible reason why your Sensi is not heating.. A reverse valve changes the direction of the refrigerant so that the heat pump can cool your home during the cooling season and heat your home during the heating season. 

If this device is stuck in one direction, it would ether cool on both the heating and cooling mode or it would heat on both cooling and heating mode


If you believe  you have a stuck reversing valve then it would be the right time to call a HVAC  professional to come and have a second set of eyes on it. Usually a stuck reversing valve is cause by a burnt or damaged solenoid which is easily replaces

3) Wrong thermostat wiring

Is your thermostat installation new? And is heating  working without problems on the old thermostat? If so, you may have wrong thermostat wiring and that could actually be the reason you Sensi is not blowing hot air.


When wiring your thermostat, make sure you’re entering the wires into the  correct terminals that correspond to your system type (Conventional or Heat Pump). 

If your old thermostat has wires attached to the following sets of terminals, the Sensi thermostat is not compatible with your system:

  • 1, 2, 3, 4
  • A, B, C, D
  • V+, VG, RS-, RS+
  • R, 1, 2, C

Make sure the OB wire is properly connected to the OB picker.

4) Ignition failure

When your furnace fails to ignite, there will be no flames to heat up the air and will eventually have no heating. This is not a problem with your thermostat but the furnace. 

 The fan could be blowing well but no hot air will blow out of the vents. Ignition Failure  could be due to a number of reasons such as lack of fuel, dirty flame sensor, closed gas.


You can head over to your furnace and check on it. You can start by checking if the gas valve is open. The gas valve should be completely open to supply the burners with adequate gas. Also if it has been a while since you refill your gas tank,you   might want to check if there is still enough gas in it.

Read also: Amazon Thermostat Blowing Hot Air On Cool [Fixed]

5) Dirty/ Defective flame sensor

Another possible issue that could prevent your furnace from igniting is a dirty flame sensor. Flame sensors help the furnace to safely operate.  They do so by sensing if there is a flame on the burners.

 If there is a  flame on burners, the flame sensor kee the gas valve open. However, if there is no flame on the burners, the flame sensors keep  the valves closed  to prevent the gas from leaking into your home which can be a health hazard.

With age, flame sensors can have dirt build up or they can become sooty. When there is too much of this on it, they won’t be able to detect the flames and thus can prevent the furnace from turning on. This eventually prevents heating and could be reason you Sensi is blowing cold air.

Read also: How to fix Nest thermostat not heating


 You can easily check the status of your furnace flame sensor by having a look at the furnace.  Flame sensors are usually cleaned when they appear to be dirty. You can use sandpaper to try and clean. But ensure that power to your HVAC system is turned off.

 If cleaning the flame sensor doesn’t fix the problem, you may consider buying a new one. But getting a new sensor  should be done only  if you have tested the flame sensor for continuity and you are sure it’s the one causing the problem.

Read: Sensi Thermostat Not Turning On AC [Fixed]

6) Damaged Ductwork

While ductwork will help distribute the heated air around your home, when they are damaged they will allow the warmer air to escape and the colder air to get in. There will be a mix of the two and this will generally lower the temperature of the air being distributed around your home. 


Inspect your ducts for possible leaks / damage. Seal them off where necessary or find a cloak HVAC professional to help you with this. The vulnerable parts of the ductwork system are the joints. That’s where most leaks occur. S inspect them thoroughly.

Read also: Nest thermostat blowing cold air on heat

Final Thoughts

Now that you have learnt what causes your Sensi thermostat to blow cold air on heat mode, we hope that this problem has been fixed. If not, we recommend you call local HVAC professionals for help.

More resources

Good Luck!

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