Why Your Furnace Is Not Kicking On When Temp Drops

Is your furnace is not kicking on when your house inside temperature decreases or drops? Your furnace thermostat sends signals to your furnace to start when the temperature inside drops below your thermostat setting. If the furnace does not kick on when the house is very cold than there is some issue which prevents your furnace from starting.

Furnace is not kicking on

Many house owners think that lack of heat indicates that your furnace is damage or broken but I have to tell you that if you face such issue then lack of heating is not always indicates that your furnace is damage or broken.

Sometimes there are minor issue which prevent your furnace from starting or furnace is not kicking on. House owners normally solve many problems like gas, power supply, thermostat and air flow without any professionals help.

Also Read: Why is my air conditioner leaking water?

Why is my furnace is not kicking on when temperature drop?

There are many issues which prevent the furnace is not kicking on. Normally, you do not need any kind of HVAC experience to solve all such mentioned problems. But if you think that you are not able or you feel uncomfortable to solve all these problems then call HVAC professional and solve this problem that why your furnace is not kicking on.

Also Read: How much does it cost to install central air?

Issue with the furnace thermostat:

Basically your thermostat sends signals to your furnace to start or stop. But, sometimes even a small problem in the thermostat cause the that your furnace is not kicking on.

thermostat issue

How to fix your furnace thermostat?

Always change your furnace thermostat batteries and make sure that you are replacing thermostat batteries before the beginning of heating or cooling seasons. Just for getting better performance without any interruptions of facing this issue like furnace is not kicking on.

Check your thermostat settings that heat option is selected means its switched on and set your temperature setting lower than your inside temperature. So, increase your temperatures by 5⁰ degree to induce your furnace to start on.

Also verify that the time or date, a.m. or pm settings in the thermostat are displayed. You must have to check that your furnace is going with the already programmed schedule. So, bypass the settings by clicking the desired temperature option button by pressing hold.

You can remove your thermostat from wall. Clean the dust which is accumulated behind your thermostat. Because this dust affecting on the sensors of thermostat. Now, gently clean all the dust with the help of paint brush or with the soft brush. Also, check if there’s any damage wires then repair all the damaged wires carefully. Because through this your furnace is not kicking on.

Issue with your furnace gas supply:

If you are using gas furnace instead of electric, then you will face issue of gas supply at many levels like you are facing issue of furnace is not kicking on and It might be possible that your house main supply of gas is interrupted because you forget to pay gas bill or there’s might be some work on gas line is going on in your area.

gas supply issue

It’s also might be possible that gas line in your furnace or the valves is off. If you are using propane, then it might be possible that your supply is low which comes under the reason of furnace is not kicking on.


Additionally, confirm that the furnace’s supply valve fully open. Also, make sure that all other gas appliances like stove, work. Make a call to utility company to verify that now, your gas bills are paid and house gas supply has not been interrupted in order to avoid this issue that your furnace is not kicking on.

Additionally, confirm that the furnace’s supply valve fully open. Follow such gas pipe which is coming out from your furnace and find that valve which is present within the 6 feet’s of furnace. Often, this valve has red or yellow lever or knobs. Your valve of gas is open if it’s in parallel position to gas pipe. If it’s in crosswise or perpendicular position, then your valve of gas is closed. Turn your handle parallel to the pipe if its closed.

Make sure that gas valve inside of your furnace cabinet is open. Follow a black metal pipe of gas which is in the furnace with a small box a switch is present on which “on” or “off” is labeled and pilot. If your furnace having its pilot light. Must ensure that button or dial is properly on. Check fuel in your propane tank, if you are using propane furnace. Make sure it full otherwise you face the issue like furnace is not kicking on.

Tripped Circuit Breaker:

Circuit breakers can be tripped just because of short circuit and due to electrical surge, defective fuse or by a fault. this is also major reason that your furnace is not kicking on. The other reason is that someone turn off the breaker by mistake and forget to turn the breaker on.

tripped circuit breakers


Typically, the Circuit Breakers are placed in your utility room, basement or might be in laundry room. Check your circuit breakers panel, there is switch labeled with “Furnace” “FAU” or the air handler. If switch indicated off position turn switch to the on position. If your circuit breakers tripped, then switch is in the middle position. Flip this switch to off position and then on switch again just to reset all the settings. If the switch trips again and your furnace is not kicking on then call your HVAC professional to diagnose this problem.

Defective circuit controller board:

When thermostat receives signals then circuit controller board of furnace send power to ignitor and the blower motor. If circuit controller board of furnace is damaged, then its unable to start the heating cycle. and you will face the issue of furnace is not kicking on.

circuit board

In few cases, the overheated circuit controller board or blower motor gives you smell like circuit burning. Then shut down your system and call your HVAC professional to solve this issue of furnace is not kicking on.


If you are having a multimeter then you can easily check voltages in the circuit controller board but use it carefully. This controller board is placed in the lower compartment of furnace which is present in the front of blower housing.

Do everything very carefully, and avoid touching any terminal to stay from electric shock.

Verify that your furnace is getting power. Some furnaces having a diagnostic indicating lights. So, when your furnace start getting power that light starts blinking. Check voltage on the thermostat across “W” and “C” terminals. Here “W” control heating and “C” is common, power supplies to thermostat. The meter will show you the rating of 24 volts if your circuit controller board works fine. then, you don’t face the problem of furnace is not kicking on.

Dirty flame sensor and pilot light went out:

The flame sensor in furnace act as a safety device which ensures that the valves of gas is open and flames are burning. If burners do not ignite then here, flame sensor automatically close the gas valve just to prevent the leakage of gas.

Flame sensors actually extend in the flames of burners which is also coated with the residue. But on other side dirty flame sensors are not able to detect the flames of burners instantly shut the gas valves off every time as it opens in beginning of the heating cycle through which your furnace is not kicking on.

dirty flame sensor

Basically issues related to pilot light also prevent the furnaces in increase the level of heating. Now a day, electronic ignitions are used in many furnaces just for light up the burners. But few old furnaces still have pilot lights. Well, pilot light is like flame which is burning constantly and ignites burners in the furnace.


Clean your flame sensors. Shut down the furnace with the switch of furnace or circuit breaker. Then remove access panel in the furnace. Basically flame sensors look alike thin bent metal rod near burners. This sensor mounted with the quarter inch hex screw which is attached to the wires.

Remove that screw, slowly or carefully take the sensor out of housing. Disconnect this sensor from electric wires. Now, gently clean such metal rod with the help of steel wool and with the sandpaper.  Don’t rub housing of white ceramic.

Now, make sure that pilot light starts burning. Pilot light normally visible through the window which is present near the base of furnace. It’s normally look alike blue small flame. But, if there’s no window present than replace such access panel and observe that pilot light. If that pilot light went out, then relight again such pilot light and check again that there’s any issue like furnace is not kicking on is present or not.

Defective Ignitor:

Modern and advance furnaces use electronic ignitor instead of pilot lights. Basically the ignitor with hot surface is a metal piece which becomes extremely red hot. Sparks are produced to fire the burners using straight spark ignitions or intermittent pilots.


Make sure that ignitor is properly working. If you are having a hot surface ignitor, then you are able to observe it. Turn off the switch on the furnace which is fixed on the unit left side. Also, remove access panel. Visually, you can easily follow a black thick pipe of gas which is going towards burners. Basically ignitor is placed behind burners and look alike thin metal in a rectangular shape. Now, lowers the temperature in thermostat just to start a heating cycle. Turn your furnace switch on and watch that ignitor. After when inducer motor starts, you will hear a hiss sound of gas and a click sound of valve opening. So, now ignitor starts heating and starts glowing red. If it does not happen, then there might be some issue with the ignitor. If you are having intermittent pilot or you are having direct or I say straight spark ignition, also you can listen the clicking sound of furnace turning on. These types of ignitions basically produce spark to light up the burners. In case, If the furnace does clicks repeatedly, then there are more chances that your ignitor is defective.

Full Condensate Pan:

Basically condensing furnace with high efficiency produces condensation which normally collects in condensate pan and then take away with the help of condensate line. So, if there’s a clog in drain pan or drain pipe then condensate pump is filled with water. So, in this result it won’t allow the furnace to turn on.


Drain all the water from pan with the help of wet or dry vacuum. Find the clog and remove such clog from the drain pan. Flip your circuit breakers or turn off your furnace. Then find a white PVC pipe which is used to exits the water from furnace to floor drain. Do a proper inspection to the proper end of drain pipe for debris then remove it with the help of brush or tools. Remove a cap from the top and flush such tube with the equal amount of hot water and vinegar. If needed, repeat the whole process.

Dirty air filters:

Air filters traps all the dust particles in the air and keep your furnace running fine and also improves your system quality. If the air filters are not changed according to schedule maintenance, then debris and dust particles are accumulated in the air filters and clog the filters. So, in this result due to clog flow of air will be restricted in the furnace and your system becomes overheated.

dirty air filters


Replace your old filters with new one. Locate such point from where the flow of air enters in furnace from returning ducts just to locate the position of filters. Take out the filter. Before purchasing new filter note the filters model size and its number. Well, filters come in many types and in sizes, also different MERV ratings.

Before inserting the filter in furnace note the arrow on the filters. Now, position such filter in a way that it’s arrow point towards the furnace. When you have to change your air filters? Many people don’t know the answer of this question and the answer is, you have to change furnace air filter after 30 to 90 days. Replace the air filters when it’s so much dirty.

Something restricting your furnace flow of air:

If you turn on your furnace, but few rooms of the house are cooler instead of others. There might be something which restricting the flow of air in the ducts and in vents too.


You have to ensure that all the dampers and all vents are properly open. Look for big dents and spaces between the parts in the ducting. If there’s any holes seal it with the metal ducts tape.

Furnace overheating and malfunction part:

For this there is a high limit switch which measures the air temperature which normally passing from furnace heat exchanger and automatically shut off your system if the system is overheating. Overheating happens when the flow air is not good just because of dirty air filters. But it also happens, because of broken heat exchanger or other broken or damaged component. Basically, in essence, the furnace is made up of numerous elements. If one part is broken or damaged, then furnace is unable to produce heat.


Change the furnace filters and call a HVAC professional to diagnose all other problems in the furnace.


There are various reasons through which furnace is unable to provide heat to your house. Issues like clogged filter, full condensate pan, dirty flame sensors and gas or power supply problems etc. If you are not able to solve all such problems by yourself, hire a professional HVAC worker in order to resolve your all problems related to furnace like fault in controller board, defective Ignitor and overheated furnace.

If you want to learn more about HVAC systems then here some articles through which you will get complete information HVAC systems.

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